I asked my friend to check this and he got the same effect so its repeteable: create dervish male char, choose haircut marked on screen below and then after max zooming out (similar to the perspective you are playing from) just start turning around. There are some flaws in his haircut, visible from different angles :/
On this screen there is one of the flaws visible in two places: on "real char" and on char's small "chose hair style" window: http://img97.imageshack.us/img97/1631/hairs1iz6.jpg - do u see "light patch" in his hairs? Hairs should be completely black.
Plz, plz, plz ANet - repair this one

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And the other problem - its not too important but maybe it has something common with bad haircuts? When I log in to my account and my chars appear there is a transparency line in my dervish head - it lasts like 1 second then vanishes and all is ok. Screenshot: http://img170.imageshack.us/img170/8038/hairs2no2.jpg