That sounds about right it does seem to happen when I'm in combat right in the middle of high speed movements and jumping around...I strafe by using shift so I'll make sure that shift+WASD, ALT+WASD, CTRL+WASD are DNP. I must be holding down shift when I'm hitting S, which would explain why my Shaman starts walking backwards and I do tend to jam the keys when I'm in combat so it makes sense.

Thanks all, I'll post again once I know how this effects my play.