No Idea What's This...

[metal_head]

I've noticed something strange...don't know if only I have this problem,and I didn't find it posted here,so I'm gonna talk about it. When I stand in certain places in the levels of my game and shoot,the projectile instead of shooting in the direction of the crosshair,there's that deviation.I mean that the projectile swings away and hit's for example the ceiling.Why is this happening,is it because of a mistake,made by me or it's just a bug?