I am having a strange bug that is starting to drive me nuts!

When I try to turn using an arrowkey, instead of my character turning in place, it goes like a car making a turn, it goes forward and makes an arc around, so it ends up a little ahead and to the side of where the character was.
This is extra annoying when walking or running, because what happens is my character turns, then turns back a little after you let go of the arrow key. I\'m very very confuzed,
Also in the death realm it means I am almost garanteed to just go off the edge, because I can\'t turn proporly so I can\'t stay on the track. Also, in the death realm I can\'t see the path in many places, it\'s too much in shadow..
Any help would me ExTREMELY appreciated!!! (is this a mac only thing?)
-thanks