SDL_ShowCursor and fullscreen

Hi,

I have implemented my own mouse cursor by hiding the real one with
SDL_ShowCursor. The problem is that when I run fullscreen the mouse
moves really slow. If I stop hiding the cursor the mouse moves normal
speed again, but of course there are two cursors.
The code works fine in a window. Is this a known problem?
I’m using Linux with Xfree86 4.0