OS X 10.10.5, Java 1.6.0_65 64-bit (I have Java 8 installed but, well), MBP early-2011.
1011 MB max allocated memory.
When I launch a world, at first memory usage is normal (18-25 %, 50~% allocated of 1011 MB).
If I exit the world and then go back, memory usage explodes, going to 80~% with 100% allocated.
When I try to exit a second time the game goes out of memory, freezes, and most of the time, crashes.
(This seems to happen only when exiting a specific save then going to any other save.)
EDIT : Also happens with other saves but less consistently.
Usually I have more than enough RAM with this 1 GB. That never happened before this snapshot.
I joined a forced crash log I did with the memory up to about 80% and a copy of the game output after one of the crashes.
I also put a game save for which the bug happens every time I log out and back in.