I was also surprised to learn that MC is approved for wet locations; all the connectors I've seen are marked "dry only."
I also note that a similar product- AC - is NOT approved for wet locations.
I am guessing that the insulated full-size groound, and the plastic (rather than paper) wrap of the wires are the reasons for this approval.
I am also guessing that the intent is to allow MC to pass through a wet location, without requiring a change in wiring methods.
