How does a Liberal become a Conservative overnight?

Ex-Liberal MP Wajid Khan recently defected to the Conservatives, presumably the political equivalent of a rat jumping onto a sinking ship.
But whatever his motives (he claims that "the Liberal Party has moved away from people like me" which is probably something of an understatement), I have to conclude that this kind of floor crossing is unequivocably wrong.
He won his Mississauga-Streetsville riding comfortably, but the constituents voted for a Liberal, not for an individual, and certainly not for a Conservative. If he believes that the riding would have voted for him as a Conservative, then he should do the right thing and resign and seek re-election in a by-election.
When David Emerson did exactly the same thing a year ago, there was much more of a hue and cry, which shows just how jaded the Canadian electorate has become. And who knows what machinations go on in the background of these events. It would not surprise me in the least if there were financial dealings involved.
The NDP have sensibly been calling for some time for a law against such floor crossing, and I for one would support that wholeheartedly.