Sometimes exp value in combat resolve screen starts from negative amounts

Like your creature would normally would have 0/50000 exp if it has just reached new level and got experience from combat that is ready to be applied,
but now combat resolve interface sometimes shows negative values instead of zero or positive,
like -154/50000 etc
It happened a few times today allready, both pre and post 0.6.0
Ill try to catch it on a screenshot next time i see it.
So far it occurs rather rarely (1/100- 1/200) and seem not to have any negative side effects.

I also saw this happen, exp bar starting from a negative value