Liberals of today are quite literally the Progressive Conservatives of yesteryear, before Preston Manning and the Reform party took "Progressive" out of their ethos by merging the Reform Party / Canadian Alliance Party into it and thus hijacking their mandate.

So really there's no irony about it. The harder right Liberals crossed over to the new Conservative party to play in Stephen Harper's sandbox. The old-guard "Progressive Conservatives" who were not comfortable moving more right moved over to the liberal party which ended up moving a little bit to the right as a result.