Also had a problem with Windows 8 that I've never had before.
I had removed my win 7 SSD from laptop, installed windows 8 on an agility III SSD (Placed in 2nd drive bay). Installed win 8 and it booted fine. Re-installed the Win 7 SSD (an M4) in drive bay 0.
Booting win 8 by changing boot priority in Bios (Samsung RF711 does not have hot key to select boot device at start up as do all my desktops) Goes with-out problem.
However if I reselect the Win 7 SSD to boot to (after booting to win8), I get the Have to run checkdisk - NOT a one time issue, boot win 8, reboot to win 7 - have to run checkdisk every time. Once run, it does not have to be re-run on subsequent boots to win 7, only If I boot to win 8.. I've done this method when having XP, Vista, and win 7 Boot disk in 3 differnt desktops and NEVER had this problem.
When creating a daul boot system in this method, none of the previous OS have messed up the Other OS Boot drives.