Comment 1 for bug 6590

Let's clarify this a bit. Your external hard disk has two partitions, which are both mounted successfully/automatically by Gnome. Then when you try to unmount one, but it does both. Is this correct? If so, then it appears that this is probably a sort of intended feature of Gnome, though maybe not.

Maybe somebody with more knowledge of what the Gnome unmounting is supposed to do and supposed to not do can shed some more light on this issue.