Problem with iTunes Match and Home Sharing

I'm in the UK and subscribed to iTunes Match as soon as it became available. My main computer is a MacBook Pro which has my entire music collection on. I have a iMac at home that acts as a music server for the house using Home Sharing and AirPort Expresses. Before iTunes Match I was able to use Home Sharing to sync my MacBook pro and iMac iTunes libraries. I had though Match would let me do the same. It will but there's a catch.

I got my MacBook library completely in sync with Match and downloaded all the matched tracks as 256kbps AAC to upgrade the sound quality of my older rips. I now want to transfer these to my iMac. I tried using Home Sharing to do this. What happens is my iMac iTunes library sees these as new tracks to match. It then flags them as duplicates. At the moment the only solution seems to be to download the matched tracks to my iMac which is what I have been doing overnight for the last couple of nights. At least I don't have a bandwidth cap or a speed cap (outside peak hours). I just wondered if I was missing a trick.