Comment 9 for bug 290415

I do confirm this behavior

I had the Problem with an usb-drive, as it did not show up in installer, i first thought it was a problem with the fact, that it was a usb drive itself.

i would suggest, to show the mounted partition and when you finally want to format/install/resize/... you get a warning with something like "On hardrive /dev/sdb following partitions are mounted: /dev/sdb2 /dev/sdb4, as for this the installer can't proceed." so the user at least knows, where the problem is