When you've been searching for months for that one bug, and you finally find it

Y u no check the log?

@busuu Maybe he means something more abstract like a bug that happens under certain conditions on the front-end. Or maybe not, lol

@busuu just solved a bug that only affected IE. Spent ages looking through did tags, making sure everything was good and proper - turns out it was caused by a function created for the old version of the program and it had only started playing up now.
Sometimes weird stuff happens.