I'm currently having the same problem. Did you ever find a solution?
My guess is that this depends on the server's capabilities. At least depending on it's capabilities the peek method sends a different command. I'm trying this with the gmail server. The server tells that it capable of IMAP4rev1.
I found also a defect that seem to match this: http://mailsystem.codeplex.com/workitem/22048
Unfortunately I'm not, yet, able to build the libs newly. Maybe a just duplicate the code locally to try it out.
Did you find a solution that you may share?