Added Version 0.5.12 . Full diff available on https://github.com/stevedoe/nxt-client/commit/024f1ce964f6545f03d0ed880c3e6e90ff9012c1
I reported the bug that lead to the release of 0.5.12.
Either CfB or I will eventually (within days) disclose the specifics regarding the issue but given the nature of the bug, it's wisest to give folks a fair chance to upgrade first.
Keep this in mind if you figure it out independently by analyzing the diff.