X dies after inactivity on Inspiron 4100

[Xaveer Leijtens <X.Leijtens@its.tudelft.nl>]

I have a problem with X 4.1 on my inspiron 4100. I use the vesa driver.
After about 15 minutes of inactivity the X server dies:

  Fatal server error:
  Caught signal 11.  Server aborting

This happens even if I switch off apm kernel support and disable power
management from the BIOS. Otherwise, suspend (apm -s) works fine, even from
within X.
I run Debian testing, kernel 2.4.16 (but older kernels had the same
problem). Details about my setup are on http://pic.its.tudelft.nl/inspiron/

Does anyone know what is responsible for killing the X server?

Thanks,
-- 
Xaveer Leijtens <X.Leijtens@its.tudelft.nl>