Mysterious doubling up of messages

We’re in the process of migrating to R8 and I’ve been slowly rolling the client out to a few users. One user is complaining (and I’ve seen it myself) about messages in her inbox appearing twice, and then disappearing again. This happens throughout the day and can usually be reproduced by hitting refresh. I open her mail file on my 8.0.2 client and I don’t have the same problem.Her client was a clean install, not an upgrade. She is not a remote user. Has anybody else seen this?