Comment 8 for bug 209408

There is a workaround -- an ugly one, but it works for me and it's simple.

If I just manipulate the user drop-down list on the "Authenticate" dialog, by just clicking on it, and then clicking somewhere else to close the list, then the rest of the desktop becomes accessible, including the Onboard on-screen keyboard (if it's already open) or the launcher on my Gnome panel.

Weird, but it will do until the patch arrives.