I am using the context module and have the masquerade block set to display in a region in the sitewide context so it will always show. Only the admin has privileges to masquerade block visibility has roles set to default (administraators). I am pretty sure context does not respect this role visibility, so it should show at all times in any event. (but I also tested using the default block system with the same results).
Anyway, when I masquerade as any user except Anonymous, the masquerade block remains visible and the navigation menu block shows the switch link to go back to admin role.
But when I masquerade as Anonymous, the masquerade block goes away, as does the navigation menu, and I am left with just the login block.
So essentially, all i did was log off with no way to get back as admin except to log back in as that role?