Summary of the bug:
sometimes (a LOT of times) Snarbolax boss does not react on hitting the bell. Even when he's biting the knight, standing right next to the bell. This can happen 3+ times in a row, and I have no idea how it triggers.

I can reproduce it at any time, though I do not know the trigger. This usually happens each time I fight snarbolax, several times per fight. Recently I defeated him 4 times in a row and had this bug happen several times in each fight.

Also, sometimes snarbolax gets "stuck" in attack frenzy, doing not 3, but 10+ bites in a row (its impossible to avoid being hit by that amount of bites, as he re-aims each and every time, can do 180 degree turns between bites, basically, hits you anywhere, range is pretty good).

Sometimes snarby bites 3-5 times in a straight line, others he bites the knight directly. I cannot tell how it works, but it seems part of his scripts were taken from alpha wolvers (after they received a limit to biting 3 times in a row), while the other part was made specifically for him, and this somehow gets in the way of the bell (while he's doing his turn-able biting, he's not affected by the bell).

Another topic with same problem:
http://forums.spiralknights.com/en/node/70408