There is a short discussion of this over in google groups
Bodies of some HTML messages downloaded via IMAP are blank - POP/IMAP and Forwarding | Google Groups

This guy sounds like he knows what he is talking about....

Dan Karp
> I'm using Windows Mobile 5 and a Google Apps account. Some HTML
> emails, when downloaded via IMAP, have blank bodies. Some of the
> problem messages have a text part; some do not. The same emails when
> downloaded via POP on this device display the message body just fine.

> Is anyone else seeing this? I can't tell if it's down to Gmail's
> implementation of IMAP on the server, or Microsoft's on the client.
> This is a major pain.



I haven't looked at the protocol-level trace yet, but I'd bet that
Gmail isn't returning the "optional" fields in BODYSTRUCTURE FETCH
responses. That seems to trigger this behavior on WM5 devices.

It took us a long time to pinpoint this bug at Zimbra.