I've an outstanding, unanswered question which I've sent to UW in a related context (IMAPD): what specific clause of the copyright is being violated, when modified versions are distributed.
Their position was that the words "permission to copy, distribute and modify" do not grant permission to distribute a modified version. In other words, they say you can distribute the software, and you can modify the software, but you can't modify it and then distribute the result. I think that, until we get a decent answer, this should be the question asked by anyone who gets a threat under these conditions: ask what specific terms of the license are being violated. You may never get an answer from the U of W, because right now the U of W can achieve its goals by saying nothing. If they have the feeling that you will let the issue slide if they let it drop, they are likely to let it drop. However, you now do have an answer to that question, so I hope you can proceed to take the appropriate action, and remove IMAPD from Main. The message I forwarded you shows clearly that they treat IMAPD as non-free software, that their position is that people must ASK for permission to release a modified version, and that the license does not give permission. That message does not give all the details. It makes sense to want to know more about the situation, but it makes no sense to let the issue slide unless and until they give you a full explanation. That is not the way to make the DFSG something that the users can rely on. If Debian decides to reject IMAPD and tells the U of W so, that will put some pressure on them to clarify the license. Otherwise they may prefer to leave it unclear in order to to "have it both ways".