Somebody else experienced the same problem as you describe, provided the savegames ans I was able to reproduce it. However, I don't know why this happens. If you provide us your savegame, we are at least able to edit the XP into it and we'll have another clue for bug fixing.

you can upload it here as an attachement to your post or send it either Yuan or me as a pm.

Here you go.

I found out, why this has happened: The affected character has fled the last battle. I think (due to a bug), when a character flees, he won't get XP until the next battle.