Setxkbmap turns off NumLock LED - but not NumLock

Whenever I use setxkbmap in a terminal (or my .bashrc), the next time I press any modifier keys (ctrl, shift, alt) the NumLock LED on my keyboard goes off, but NumLock itself is still active so it's in some kind of inconsistent state. If I now press NumLock, the LED stays off but NumLock turns off, and a second press on NumLock turns both the numpad and the LED on again. Curiously, while the LED is in this inconsistent state, pressing caps lock turns both the NumLock and CapsLock LEDs on. The command that I have in my .bashrc causing this is setxkbmap -option compose:ralt but it also happens if I issue a plain setxkbmap with no parameters, or do anything else with that command. Why is this happening (and am I doing something wrong)? Dump of Xorg -version(I'm running Xubuntu/XFCE): X.Org X Server 1.7.6 Release Date: 2010-03-17 X Protocol Version 11, Revision 0 Build Operating System: Linux 2.6.24-30-server x86_64 Ubuntu Current Operating System: Linux xxxxx 2.6.32-41-generic #94-Ubuntu SMP Fri Jul 6 18:00:34 UTC 2012 x86_64 Kernel command line: BOOT_IMAGE=/boot/vmlinuz-2.6.32-41-generic root=UUID=xxxxx ro quiet splash Build Date: 25 February 2012 06:57:33AM xorg-server 2:1.7.6-2ubuntu7.11 (For technical support please see http://www.ubuntu.com/support) Current version of pixman: 0.16.4