F10 to F11 upgrade loops at Finishing upgrade process

[Colin Paul Adams]

I'm currently upgrading my main desktop from F10 to F11 (both x86-64).
It is currently saying:

1613 of 1613 packages completed

Finishing upgrade process. This may take a little while...

It has already taken a very long while (probably as long as the 1613
packages took). The progress bar marker is flicking backwards and
forwards in what appears to be approximately a 3-second loop.

What can I do about this? My only guess is Ctrl-alt-del and hopes it
does the right thing on reboot - but this is a desperate hope.
-- 
Colin Adams
Preston Lancashire