I also experience the same issue. LW 2.3.1 will only quit when I force-quit it through OS X. I was able to get around this by selecting "Force Quit" Under Preferences : Shutdown (though it appears to not work occasionally).

I have also noticed a discrepency with the help FAQ and the 2.3.1 LW version where the media player is NOT in the tools menu. There are also some issues with window redraws. When is the next scheduled release - I heard of someone mentioning 2.3.2, but I just downloaded this program last week. is 2.3.2 really out and does it fix some of the latter issues mentioned?

Cheers