Answers.Body: <p><a href="https://i.sstatic.net/4vdYn.png" rel="nofollow noreferrer"><img src="https://i.sstatic.net/4vdYn.png" alt="enter image description here"></a>There must be an issue with your copy of Arena 3.5.1 because Stockfish found a mate in 20. I'm using Scid for my GUI. I have attached the moves. </p>
  
Answers.ContentLicense: CC BY-SA 4.0
Answers.CreationDate: 2018-12-10T23:49:03.360Z
Answers.Text: No there was no issue. OP had been making moves, there was not enough moves left for checkmate.
Answers.UserDisplayName: SmallChess
Answers.ContentLicense: CC BY-SA 4.0
Answers.CreationDate: 2018-12-10T20:02:25.280Z
Answers.LastActivityDate: 2018-12-10T20:02:25.280Z
Answers.UserDisplayName: Beschravi
Answers.Body: <p>This is <strong>not</strong> a blunder, expected behaviour from the engine. Everything worked as intended. Try to copy the FEN string out, and you'll know.</p>
  
  <p>Although the position looked winning, White didn't have enough moves to force checkmate before the 50 moves rule. Stockfish, knowing the position was a dead draw immediately asked for simplification.</p>
  
  <p>The position you had is 100% equal, there was <strong>no way</strong> to win it. It's a draw. What Stockfish did was not wrong.</p>
  
  <p>If the Tarrasch program didn't send out the 50 moves counter to Stockfish, you'd never get the problem on Tarrasch. If that was the case, it was an error in Tarrasch because the 50 move counter is part of the game.</p>
  
  <p><strong>Solution?</strong></p>
  
  <p>Setup a new board with the same position but reset the 50 moves counter.</p>
  
Answers.ContentLicense: CC BY-SA 3.0
Answers.CreationDate: 2018-02-16T14:33:43.253Z
Answers.Text: Mind boggles. B+N checkmate doesn't take 50 moves so how did it get into this situation in the first place?
Answers.UserDisplayName: Joshua
Answers.ContentLicense: CC BY-SA 3.0
Answers.CreationDate: 2018-02-16T14:42:43.727Z
Answers.Text: @Joshua If you played the moves on the board but unable to checkmate yourself. On your 49th move, you turned on Stockfish for advice. Too late for checkmate!!
Answers.UserDisplayName: SmallChess
Answers.ContentLicense: CC BY-SA 3.0
Answers.CreationDate: 2018-02-16T23:19:27.297Z
Answers.Text: This seems plausible but how do you and the 19 upvoters know this is the case here?
Answers.UserDisplayName: JiK
Answers.ContentLicense: CC BY-SA 3.0
Answers.CreationDate: 2018-02-17T00:36:31.740Z
Answers.Text: @JiK Did you see the answer below? "Apparently there was a move counter from a previous game or analysis that got somehow applied to the new position".
Answers.UserDisplayName: SmallChess
Answers.ContentLicense: CC BY-SA 3.0
Answers.CreationDate: 2018-02-17T03:24:06.200Z
Answers.Text: @SmallChess.   Yes, the problem I was having with Arena was that I was setting up a new position after analyzing a variation.  There is a field called "number of half-moves" which is preset to the number of moves in the variation you just finished.  In order to really start with a clean slate, you either need to clear that field, or delete the entire variation before doing the new setup.  Thank you (stack accounts now merged!)
Answers.UserDisplayName: Larry
Answers.ContentLicense: CC BY-SA 4.0
Answers.CreationDate: 2019-03-16T18:23:46.537Z
Answers.Text: its been shown that with perfect play and certain positions, B+N checkmate can take over 50 moves,  But it is possible.
Answers.UserDisplayName: john k
Answers.ContentLicense: CC BY-SA 4.0
Answers.CreationDate: 2021-02-09T15:13:01.190Z
Answers.Text: @john, the max needed to checkmate from any position with N and B against lone K is 34 (I've seen claims for 32-33 as well). Other endgames (like Q against B+B requires at most 75 moves) may need more. These assume optimal play from either side. In practice, it's often much smaller or higher, depending who blunders first or who's short on time.
Answers.UserDisplayName: Abel
Answers.ContentLicense: CC BY-SA 3.0
Answers.CreationDate: 2018-02-16T03:37:36.873Z
Answers.LastActivityDate: 2018-02-16T05:57:30.993Z
Answers.LastEditDate: 2018-02-16T05:57:30.993Z
Answers.UserDisplayName: SmallChess
Body: <p>Using stockfish_8_x64 with Arena 3.5.1, I see a weird pick by Stockfish.  Start here: <a href="https://i.sstatic.net/T5BOT.jpg" rel="noreferrer"><img src="https://i.sstatic.net/T5BOT.jpg" alt="Position"></a></p>
  
  <p>White, Stockfish, to move.  It plays bb6-g1,losing the bishop and the win.  </p>
  
  <p>Also strange:  the same engine does not make this weird move in the Tarrasch program.  Playing with KBN against K, I've seen Stockfish often blunder away the advantage in these endgame setups.</p>
  
  <p>Any clue how this could be happening, or why it would happen only with Arena?</p>
  
  <p>EDIT:  SmallChess answer is correct.  The problem was a residual, non-zero value in the position "number of half-moves" setting.  See my reply to his posting for more information.</p>
  
Comments.ContentLicense: CC BY-SA 3.0
Comments.CreationDate: 2018-02-16T23:17:05.630Z
Comments.Text: @Larry: I think you have multiple accounts; that's why you're not able to accept the answer. Some moderator should be able to merge your accounts and then you should be able to accept.
Comments.UserDisplayName: ShreevatsaR
Comments.ContentLicense: CC BY-SA 3.0
Comments.CreationDate: 2018-02-17T00:39:28.127Z
Comments.Text: @ETD Can you please help?
Comments.UserDisplayName: SmallChess
Comments.ContentLicense: CC BY-SA 3.0
Comments.CreationDate: 2018-02-17T03:29:20.317Z
Comments.Text: Thank you @SmallChess, I was able to resolve this on my own.  I'm good at IT, not so good at chess :(   BTW I downloaded your program, it is a masterwork.  Thank you.
Comments.UserDisplayName: Larry
Tags: <endgame><stockfish><blunder>
Title: Stockfish blunders away a piece
ThreadText: # Stockfish blunders away a piece
  
  (Asked by: username_0 on 2018-02-16)
  
  Using stockfish\_8\_x64 with Arena 3.5.1, I see a weird pick by Stockfish. Start here: [![Position](https://i.sstatic.net/T5BOT.jpg)](https://i.sstatic.net/T5BOT.jpg)
  
  White, Stockfish, to move. It plays bb6-g1,losing the bishop and the win.
  
  Also strange: the same engine does not make this weird move in the Tarrasch program. Playing with KBN against K, I've seen Stockfish often blunder away the advantage in these endgame setups.
  
  Any clue how this could be happening, or why it would happen only with Arena?
  
  EDIT: username_2 answer is correct. The problem was a residual, non-zero value in the position "number of half-moves" setting. See my reply to his posting for more information.
  
  **Tags:** endgame, stockfish, blunder
  
  > **Comments:**
  > **username_1**: @username_0: I think you have multiple accounts; that's why you're not able to accept the answer. Some moderator should be able to merge your accounts and then you should be able to accept.  
  > **username_2**: @ETD Can you please help?  
  > **username_0**: Thank you @username_2, I was able to resolve this on my own.  I'm good at IT, not so good at chess :(   BTW I downloaded your program, it is a masterwork.  Thank you.  
  
  ---
  
  ## 2 answers
  
  ### Answer by username_2 on 2018-02-16. Score: 30 | Accepted answer
  
  This is **not** a blunder, expected behaviour from the engine. Everything worked as intended. Try to copy the FEN string out, and you'll know.
  
  Although the position looked winning, White didn't have enough moves to force checkmate before the 50 moves rule. Stockfish, knowing the position was a dead draw immediately asked for simplification.
  
  The position you had is 100% equal, there was **no way** to win it. It's a draw. What Stockfish did was not wrong.
  
  If the Tarrasch program didn't send out the 50 moves counter to Stockfish, you'd never get the problem on Tarrasch. If that was the case, it was an error in Tarrasch because the 50 move counter is part of the game.
  
  **Solution?**
  
  Setup a new board with the same position but reset the 50 moves counter.
  
  > **Comments:**
  > **username_4**: Mind boggles. B+N checkmate doesn't take 50 moves so how did it get into this situation in the first place?  
  > **username_2**: @username_4 If you played the moves on the board but unable to checkmate yourself. On your 49th move, you turned on Stockfish for advice. Too late for checkmate!!  
  > **username_5**: This seems plausible but how do you and the 19 upvoters know this is the case here?  
  > **username_2**: @username_5 Did you see the answer below? "Apparently there was a move counter from a previous game or analysis that got somehow applied to the new position".  
  > **username_0**: @username_2.   Yes, the problem I was having with Arena was that I was setting up a new position after analyzing a variation.  There is a field called "number of half-moves" which is preset to the number of moves in the variation you just finished.  In order to really start with a clean slate, you either need to clear that field, or delete the entire variation before doing the new setup.  Thank you (stack accounts now merged!)  
  > **username_6**: its been shown that with perfect play and certain positions, B+N checkmate can take over 50 moves,  But it is possible.  
  > **username_7**: @username_6, the max needed to checkmate from any position with N and B against lone K is 34 (I've seen claims for 32-33 as well). Other endgames (like Q against B+B requires at most 75 moves) may need more. These assume optimal play from either side. In practice, it's often much smaller or higher, depending who blunders first or who's short on time.  
  
  ---
  
  ### Answer by username_3 on 2018-12-10. Score: 2
  
  [![enter image description here](https://i.sstatic.net/4vdYn.png)](https://i.sstatic.net/4vdYn.png)There must be an issue with your copy of Arena 3.5.1 because Stockfish found a mate in 20. I'm using Scid for my GUI. I have attached the moves.
  
  > **Comments:**
  > **username_2**: No there was no issue. OP had been making moves, there was not enough moves left for checkmate.  
  
  ---
  
  