Fedora Core 2 Test 3 installer Chose upgrade, the installer complained I didn't have enough space, went back, chose reboot on the "do you have all needed media" screen. The system didn't have modprobe.conf after the upgrade, anaconda needs to restore the file when the user aborts.
My upgrade completed successfully, but my modprobe.conf file was empty. The .anacbak file was still there.
I copied the .anacbak file back into place and it worked fine. So the problem is broader than just backing out of an upgrade.
Fixed in CVS