That's something I haven't heard of and if I had to guess (and I think I do), I'd say it's something at your end, rather than with the server.
Experiment with Outlook Express until you can detect a pattern. For instance, turn the preview pane on if it's off (or vice versa).
Also check Options to see the delete from server settings and change it so mail isn't deleted for three days--and see if your problem changes.
All the best,
Allegedly Famous Book Author: PC Annoyances