are you sure that this is a bug and is not intended in any way?
When done properly, there is supposed to be a last phase which is a burn phase. Everyone spreads out and attacks the boss. You completely skip this phase when your DPS is so low that the boss enrages before all of the tentacles are dead. Some say that it is a bug and that it is impossible to kill all of the tentacles before enrage- well... we did it with nearly a minute left to spare. That proves that there is no bug to the enrage timer.