Doing a USB hard-drive upgrade of F10 to F11 on i386 (meaning boot from a USB flash drive with a copy of the ISO on it, tell it to do a hard drive based upgrade) System drive is /dev/sda. USB flash drive is /dev/sdb1 Upgrade fails with this error: "Dirty File Systems The following file systems for your Linux system were not unmounted cleanly. Please boot your Linux installation, let the file systems be checked and shut down cleanly to upgrade /dev/sdb1 OK" The filesystem dirty check should ignore the install media
We'd rather be safe than sorry here. If your install media was not properly unmounted, you could end up with screwed up packages that could lead to serious installation problems. This is a similar sort of check as media check for optical media - it doesn't detect all possible problems, but it stops a fairly obvious and easy to hit class of bugs.