I have noticed in build 657 and now 660 that the cursor jumps around erratically at unpredictable times. Here are some of the symptoms I have seen:
If I have folded everything in my Java file using and start typing a new method, everything un-folds when I hit the enter key
When I am just typing in my Java file and not really watching I'll suddenly notice that the cursor has moved off (I think after I hit the backspace key) to some place totally disconnected. I had noticed this bug a long long time ago. It seems to have re-surfaced.