Originally Posted by Drip

Dunno, I never use a gather right after a level up, but just spend all my stamina before that, and never ran into this. So perhaps the problem is the combination of levelup and gather in a row, that one of the two adds to the old stamina value instead of the new value. Once you're in overflow, a gather won't add on top of that anyway. At least, it shouldn't from what I recall.

I neglected to mention having spent stamina to get below the cap before gathering.