Painful
Yesterday, I came down with a painful malady most developers have learned to fear -- a critical bug that disappears when the debugger on and manifests itself only in the release build. Worse, it crept in quietly under the cover of darkness: I have to go all the way back to August 30 to find code that's not afflicted.
This one has all the hallmarks of a one-line bug. In fact, it's probably a one-character bug: an "x" that should be a "y". But I spent an entire day on it, and I was up before dawn this morning to get a head start on pinning it down.