Check your characters' fire resistance. I re-loaded a save just after exiting the chieftain's hut and attacked a tibar to turn it hostile. About 80% of its attacks missed, and those that hit only did from 10 to 20 fire damage.
Also, check the tibars' level (they were level 9 in my game). If you are not particularly vulnerable to fire damage, then they may be unusually tough for some reason.
Do you have the
patch installed?
Is the crystal bag working normally? A glitch with the crystal bag should only effect one character, though...