As a player in Lavinia's group I have to say that I was rather surprised at the harsh reaction a mere 50XP less were causing, especially considering that the average XP total for that session was near 2000XP.
It's quite normal to award XP for good role-playing, paying attention to the DM and or making everyone having a good laugh in our group. We had a good time throughout the adventure but when she handed out XP the atmosphere was instantly poisoned.
Some players start feeling punished when others get more XP than they do and somehow I feel that the discussions would have come up even if she would have awarded bonus XP in the single digits. As for me, I'm no longer willing to put up with this player's bahaviour and next time something similar happens I'll vote for kicking him out.
~Marimmar