xmodmap auto-disabling?

[John Coppens]

Hi people,

I'm experiencing a strange thing.

I first thought that .Xmodmap was not being activated, but then I found
that, even when executing xmodmap .Xmodmap (which works correctly),
after some time, the commands from the file are lost (disabled).

In my case, the main problem is the definition of the ComposeKey.
Executing the above command enables it, and it works in all programs,
even terminals. But then, suddenly, it stops working. No reboot, no
exiting my account, not even closing or opening other windows. 

Could there be something that re-inits the X11 system, disables the
modmap, or maybe something in XFCE which could cause this?

Thanks for any ideas!

John