Fistfight: Apple mail.app and IMAP

So I'm trying to get Apple's mail.app to work with an IMAP provider, but having some serious issues with it, and I think it's something going on with Mail. Across multiple service providers - AppRiver, FuseMail, and others - everything sets up and works fine. I can send and receive mail, create and delete IMAP folders, everything. However, when I try to drag-and-drop a set of folders from my Mac onto the IMAP-hosted folder hierarchy, it'll copy a subset of the folder content and then choke, leaving the other folders blank or not copying them at all.

In specific, say you have the folder A, and inside of it, you have folders B and C, and all of these folders contains multiple e-mail messages. If you drag it from Mail.app into an IMAP or Exchange server, it'll copy all three folders, but only copy the contents of folder B. Folders A and C will remain empty, even after hand-forcing a sync for the server, relaunching Mail.app, and/or multiple rounds of swearing.

The only service provider that I've found to date that works fine is - surprise - .Mac mail. I've been able to recreate this other behavior across two Apple machines, both Intel and PPC, so I'm pretty sure it's here to stay. I've giving it about 2-3 more days of poking around mail servers, and then I'm going back to (cough) POP for a while.

Update: First call to AppleCare lasts 25 minutes, of which I speak to someone for a total of 3-4 minutes, who has realistically never heard of Apple Mail, much less IMAP - and then puts me on indefinite hold. Second call to AppleCare lands me in the lap of someone who, when I say "I'm copying folders from my local Mail folders onto an IMAP server, and they're not completely copying", says "Are you connecting to the server from Safari, or from 'Go to Folder' in Finder?"

Update: Apple's suggestion is to re-email myself all of my old e-mail to the new server. *cough*