I can actually see it from his point of view - he has a flat in London, that we pay the mortgage on. Then the rules change and they can't get mortgage payments, only rent.
What does he do? Sell it? Probably at a loss - and while you probably would like the idea of Jim taking a personal hit, it goes against the reason MPs get these payments - to enable anyone, from any background, to represent their constituents in far away London. He could have set up a company and sold it to that, and then rented it off the company, but I'm not sure how legal it would be and it looks even more dodgy
I would have changed the rules to say that mortgages are fine, but any profit made on sale is given back to Parliament, and the flat is sold/passed on to another MP if you lose your seat - the mortgage is held by the nation.
Either that or just bung them all in University style Halls of Residence
Here's a scary thought, if wee Eck wins in 2014, I bet you Mr Murphy will be back up here, shoving Johanne Lamont under a bus (or Anas if he has taken over by then), vying for the top job.