nnimap out of sync

[Kurt B. Kaiser]

I'm running ngnus-0.6, and so is my wife. We're using nnimap to access
various imap servers.

Her gnus has got out of sync with the imap server on at least one group.
The webmail shows articles that gnus doesn't show in the Summary, and
the Summary (when opened with C-u) shows read headers for articles that
are no longer on the server.  Restarting everything doesn't help, and
neither does unsubscribing the group or killing it.

I used an alternate imap app to access the server, and its headers agree
with the webmail.  So it appears to be a problem with my gnus.

She doesn't have a lot of email unread or ticked, but she does have
around 6000 read emails and I was starting to sort the important senders
(e.g. her mother) into different folders using limiting when I first
noticed the problem: an author limit followed by a multiple move (around
300 items) resulted in gnus running an expiry on the whole 6000 emails
for each item moved.  That was going to take forever, so I interrupted
it.  I don't know whether this initiated the problem.

She was running 0.2 at the time, so I upgraded her to 0.6 hoping that
might help, but no joy on the sync issue. (I haven't tried yet to see
whether upgrading solved the exponential move time issue.)

I've been using gnus for many years and never had a problem like this
before.

Two questions: 

1. How do I regenerate the data, i.e. get gnus to sync to the status of
   the items on the server? C-u g in the Group buffer doesn't do it.

2. What might have happened to cause this?

-- 
KBK