weird multi-boot problem

This is a new one. I swear I've done this before with no problems since installing RC2, but now when I boot into RC2 and run normally for a while, then restart the system and boot into Fedora Core 5 instead, the FC5 initial fsck always reports a corrupted superblock on a big partition I have on my 2nd disk drive (always the same partition). If I shutdown all the way (power off), and restart from power up booting to FC5 I don't get any corrupt superblock messages (all partitions on this system are ext3). So it isn't really corrupt, it just looks that way when I soft restart. Don't know if the sata drivers on suse are leaving the disk in funny state or what.