X remote makes mouse disappear

When I connect my laptop to my PC for remote X (my laptop is rather old so I
use the power of my PC) almost everything works as expected. Screensavers,
mc..
But some programs do a nasty thing: my mouse on the laptop dissappears, and
I need to restart XFree on my laptop again. Those 'nasty' progams are
Mozilla, Gimp among others.
Logs on both Xserver and Xclient don't tell anything.
Perhaps the problem is that on the laptop 2 mice are connected,whereas on
the PC only one.
But still I wonder why some programs don't and others do make my mouse
dissappear. Without any trace left. Using Mandrake 9.1 on PC, Slackware 9.1
on laptop. XFree 4.3 on both.
I am clueless, if just anyone could give me a hint. Using Google groups
didn't help. So I guess there is some kind of bug in XFree4.3.
Thanks,
Arne