[Potential Bug] Defeat Marion - XP Cap

While playing, and replaying repeatedly, the "Defeat Marion" quest, instead of the XP award being reduced for enemy kills once it reaches a certant point, all XP awards above the kills remains the same after reaching 10k, but none are actually added to my overall total. This isn't a matter of "lag" with it being posted either as it remains at that total for the entire duration (5-10min later, or after going back to a city, still that amount). I don't know if there is an intentional "hidden" cap or not, but this is the first time I've encountered something like that.