What was the worst bug you've ever solved ?
sgoraya: This bug was solved after the title went gold and shipped in US :/  We did not find out about it until a few users emailed us.  The bug got through SONY and our internal testing...-It was a first gen PS2 game that had to get pushed out since it was considered a launch title.  The dungeons in the game were seeded and randomly generated - In some instances, a lever to proceed to the next dungeon was made inaccessible due to the random seed that enclosed the lever with 'wall' tiles - the player either had to start the game over and hope the dungeon was seeded correctly, OR play through the game without finishing that particular dungeon.  It was not total killer in the sense that the game could still be completed, but it was tough to know that such a glaring bug got through...-Fix was made for the Korean version :)
Basically a check to make sure that wall polys did not enclose any levers prior to generating the dungeon, if the lever was bounded, re-seed, generate and check again...