I could be wrong - but it's not clear (at this point) that it is not an issue with the IMAP server rather than the client. I have not had issues with header display with uw-imap server, and I have not read others (with mainstream imap servers) having the same problem. That leads me to think it *may* be janaserver.....
It may not be easy - but you might want to try to test with other imap server(s) and see if that makes the difference?