So naturally Wajid Khan's fellow Liberal MPs are irate over his appointment as a special advisor to Stephen Harper on the Middle East and Afghanistan.
Yet it's difficult to see what parliamentary or constitutional convention has been violated here. Khan is not joining the government as a minister; he will not be making final policy decisions, nor will he be binding himself to vote with the Conservative government on said policies.
No rule or convention has ever prohibited the government of the day from seeking the counsel or advice of members of the opposition. If any such rule existed, parliamentary committees would be powerless to recommend changes to legislation, and other parliamentary business would be more difficult if not impossible.
Stephen Harper thinks that Wajid Khan has particular expertise and insight that is lacking in his own caucus, or else why would he have made the appointment? He is empowering an opposition MP, not simply out of partisan political considerations (though those are present too)
This appointment, in fact, is a small step to bridging the democratic deficit that the Liberals were always pledging to remedy.