Another problem with the co-habitation argument: canonical

One more nail in the coffin:

Michael Lawler and Gail Risch (U.S. Catholic on-line) propose to treat certain co-habiting couples essentially as married. This bad idea should, and will, go nowhere (Abps. Charles Chaput and Elden Curtiss and folks like Carl Olson see numerous problems with it), so I need not comment much on it. I should point out, though, that L&R's presentation of the canon law on marriage is problematic in several respects.

[How?]