I went through diffs once again, without noticing anything especially suspicious, but there is still hope in brute force. If you are willing to dedicate some time to it, we could try bisection. There are 22 commits between 20121220 and 20130321, so I would provide 23 builds (that extra 1 as sanity check) and you would track down the commit which introduced the bug. 23 might not sound encouraging, but with binary search you should be able to find the problematic commit in about 5 attempts.