the question i have about matt being the master is this:
a couple of episodes ago we saw matt e-mail himself information about the kanima off of alison's computer tyo hiself. This would elad us to believe that up until that point he was not the one controlling it, its like he was searching for information himself ansd since alison had it realised its what he was looking for and took it.
That would raise suggest that there is more than one master and even, to me anyway that the master may not be set. Perhaps somehow the master can change.