Mail.app and the constant IMAP refresh … why, oh why?

I’ve noticed that Mail.app feels the need to refresh my IMAP cache for each of my Google Mail accounts from time to time. That works out to a huge amount of data transfer for no apparent reason and I can’t figure out why it keeps doing that? Thunderbird seems to do something similar but it maintains an index of what has been synchronised and only downloads what it needs to. Mail.app doesn’t seem to have that index in place or, if it does, the index seems to expire or something.

I don’t claim to understand IMAP all that well or why various things like this happen. I can’t seem to find any information about this online so I just steer clear of Mail.app and either use the Web-based Google Mail directly or I use Thunderbird (which has the added benefit of return receipts which come in handy). There are a couple features in Mail.app which appeal to me including the data detectors which make it pretty easy to add or update contacts. The downside is this download behaviour consumes a huge amount of bandwidth and in our bandwidth constrained environment, that is a big #fail!

Does anyone else experience this? Any ideas, suggestions? Should I just ditch Mail.app until Apple releases a decent version?