Vaguely reminds me of the testing issue I dealt with a few years ago as end user QA. Dev team kicked us more than a dozen builds that had some some graphics glitch blocking the very last puzzle. Each time they said they had fixed it, and each time we sent it back to them saying it was exactly the same as before. Recoded entire sections of the whole thing, added massive error checking, and burnt weeks of dev time sorting it out.
Then someone realized the guy fixing the bug wasn't properly merging his code with the QA build branch... Reverted and properly merged, and the original fix actually worked.