Bug requires 2 developers, full-time for 4 days to trace, debug, scratch heads, analyse logs. Third developer helping occasionally. Finally identify fix. Fix is 2 lines. D'oh.

Sounds like most of the legacy code I work with.

2 lines can be disastrous. I once fixed a bug that was cancelling valid POS transactions because the guy put != instead of ==. So i just had to change it and it still works atm.

had the same last week

1st line in the function was return null;
figured that one out quiet fast, only to find out that 20 lines later int he same function there was another return null;
found that one 6h into the bug fix, no IDE, was directly on production because the versioned copy was already debugged a gazillion times