[xmonad] xkb, xmonad and mouse accessibility

Hi, I like to use the keyboard to control the mouse, using a feature I was told belongs to a module of X ('xkb', I think). I press Alt-Shift-NumLock and then the keypad controls the mouse. After some time using that inside xmonad, it stops working, and I have to activate it again. Do you think that can be caused by xmonad? Or I should search only for X information? Thanks, Maurício