nnimap mails being marked old before I ever see them

[John Sullivan]

This problem has been bugging me for a long time, but it's recently
caused me to miss some important e-mails, so it's vital that I figure
out how to work around it or ideally to fix it.

First, new mails arriving are sometimes instantly marked "O", so I never
see them unless I expand with / o. This seems to happen when I have a
group open for a long time, so that it has to reconnect to the imap
server when I finally do an operation on a message. Whatever messages
arrived in the meantime will never get seen.

Second, mails that have been sitting visible and unread for a while will
at some point randomly be marked O as well, and disappear from view
unless I expand with / o.

This is with Gnus v5.13, a courier IMAP server, and the nnimap backend.
However, while I have seen the problem with nnimap talking to my local
IMAP server as well, it happens much, much, much more often with a
different courier server that I talk to over the network. 

Any help, debugging pointers or workarounds (can I stop messages from
ever being marked O?) would be much appreciated. I'm current working
around the first problem by running a separate script that spits out
subject headings as mail arrives, and working around the second problem
by using a lot of the ! mark -- since that keeps the mail visible, but
they are not working perfectly and are far from ideal.

Thanks,
-- 
John Sullivan
Emacs Planner Maintainer
http://wjsullivan.net/PlannerMode.html
GPG Key: AE8600B6