In Tuesday's beta release we tried to fix a collision bug that had been reported, but the fix had some unintended side-effects that could produce false-positive collision events. This is the kind of thing that can break a lot of games, so we're releasing a patch to correct the issue. Hopefully with the adjusted fix the original problem is solved without any of the unintended side effects. If you ran in to any issues with r257 please check again with this release - and if you still have trouble, please file a new bug.
We'd like to bring these updates to a stable release soon. Assuming all works well, we'll leave it a week or two for confidence everything is working, and then hopefully we can bring it to the stable channel.