I thought the game keeps track of excess xp which is then given to you when you import the save game...but I just checked some of my saves using a save game editor, and the xp amounts dont match up.

My main character had 177k xp before fighting the undercellar assassins in chapter 6. Yet, my auto-save when entering the temple of bhaal shows me with 163k xp so something doesnt match up here...it seems the game reset my xp count somewhere in between.