Did you try this to confirm that the sub event won't fire?
I'm not positive, but I thought that once the main condition is met then all events and sub events proceed even if something happens to counter the original condition.
Event: Buttmode == True
etc conditions...
Main Event Actions: ButtPoints += 10
ButtMode = False
Sub-Event: ExtraButt == True
Sub-Event Actions: ButtPoints += 1000
The condition that would be messed up by what you describe would be something like a while condition.