you hit a mob and it turns white for a millisecond, in order to show you, that it got hit. nice feature.
but if you have 20 mobs, the entire screen flickers like crazy. unfortunately there are people like me who overreact on that with heavy headache after several min. - maybe you heard about people who can't stand flickering discolights for long - it's the same effect.
is there any possibility to turn the flickering off?