Hung in XOpenDisplay(:0), aborting

Binary package hint: xorg-driver-fglrx

Whenever a user logs out of KDE, X is being restarted and fails:

May 25 23:05:11 localhost kdm: :0[13667]: (pam_unix) session closed for user who_logs_out
May 25 23:05:13 localhost kernel: [275266.564840] [fglrx] total GART = 130023424
May 25 23:05:13 localhost kernel: [275266.564911] [fglrx] free GART = 114032640
May 25 23:05:13 localhost kernel: [275266.564915] [fglrx] max single GART = 114032640
May 25 23:05:13 localhost kernel: [275266.564918] [fglrx] total LFB = 134217728
May 25 23:05:13 localhost kernel: [275266.564921] [fglrx] free LFB = 119828480
May 25 23:05:13 localhost kernel: [275266.564924] [fglrx] max single LFB = 119828480
May 25 23:05:13 localhost kernel: [275266.564927] [fglrx] total Inv = 150994944
May 25 23:05:13 localhost kernel: [275266.564930] [fglrx] free Inv = 150994944
May 25 23:05:13 localhost kernel: [275266.564933] [fglrx] max single Inv = 150994944
May 25 23:05:13 localhost kernel: [275266.564935] [fglrx] total TIM = 0
May 25 23:07:11 localhost kdm: :0[23070]: Hung in XOpenDisplay(:0), aborting
May 25 23:07:11 localhost kdm: :0[23070]: Cannot connect to :0, giving up
May 25 23:07:11 localhost kdm[13664]: Display :0 cannot be opened

After that, the machine needs to be rebooted to get X working again.
This only happens when using the fglrx driver. The free ati/radeon driver doesn't expose this behaviour.