I discovered this problem, after a Fedora 10 upgrade (from 9) on both my Dell Latitude D610 laptop and my Dell desktop with Kinesis USB keyboard. I had issues with some control keys sending incorrect keycodes (e.g. left arrow sent Alt_R, Alt_L sent Delete and up arrow send PrintScr... there were more). The solution for me was to set the 'Keyboard Model' in gnome-keyboard-properties to 'Evdev-managed keyboard' and everything's fine. Changing the 'Keyboard Model' back (to 'Dell Latitude Series Laptop', for example) reproduces the problem 100% of the time.
That is not a bug. X is using the evdev driver, thus "Evdev-managed keyboard" is the correct configuration.