Lucid switch user escape problem

[Colin Law]

On Lucid the shutdown menu shows a list of users.  If I select one of
those by accident and don't know the password there seems to be no way
of getting out of the login screen, other than restart.  Cancel just
shows the same screen again (with only the selected user shown).  Am I
just blind and cannot see an obvious button or is this a bug?  I can't
see anything on launchpad about it.

colin