Version 0.6.6 is minor update that adds some custom cave and crystal dungeon art for stairs and entrances. There are also some minor optimizations and one possible fix for some broken movement bugs.
A number of people have reported freezing up after using cauldrons, I've been unable to reproduce this issue but have added some additional logging that might help track down the issue. If you do encounter this bug - or any other - please do file a bug report with a recent save game if possible.