Mac iTunes keeps adding the wrong files to my playlist 2011 iMac, OSX Mavericks, iTunes 12.6.1.125

I'm a musician and am working on finalizing my new EP.  I have the master .wav files in iTunes, which I then convert to .mp3 to send to some people for feedback etc.  I have two playlists, one which contains the .wav files and one which is supposed to contain the .mp3 files, but that's where I run into trouble.

I can select the .mp3s and add them to the playlist in question via any means - drag &amp; drop, right click, etc.  Regardless, what actually ends up in the playlist, is the .wav files.

Obviously these files have the same names except for the extension, since iTunes created the .mp3s from the .wavs.

Why on earth does iTunes insist on adding the .wavs to the playlist instead of the .mp3s I have selected?  And how can I fix this?
While not answering the why part of my question, I was able to solve the problem by deleting the .mp3 playlist entirely, selecting the tracks in question, and adding them to a new playlist again.  Now the correct files are in the correct playlist.