How to regenerate random smart playlist in iTunes 11? I have several smart playlists that pick a random selection of music limited by total disk space.

It used to be that to change that random selection, you just selected all the tracks in the smart playlist and pressed backspace to delete them, which caused it to repopulate with a new random selection. 

In iTunes 11.1.5, if I select all the tracks and press backspace, nothing happens.

How am I supposed to regenerate the random list now? The only way I've found that works is to open the smart playlist properties, change the "selected by" dropdown to something other than what I want, click OK, then open the properties it again and change it back. But that's far from optimal.

EDIT: Apple seem to have fixed this sometime around iTunes 11.4. You can once again select some or all of the tracks in a Smart Playlist, then press backspace to delete and regenerate (provided Live Updating is selected in the playlist properties).
If you uncheck "Live updating" in the smart playlist edit screen you will be able to delete tracks from the smart playlist. 

However the playlist won't repopulate until you right-click the playlist and select "Update Smart Playlist".

Interestingly that command doesn't do anything unless the tracks have been deleted.