A few thoughts as a habitual backpack wearer...
A partially removed backpack is a lot more dangerous than one just worn. I suspect it is the loose hanging buckles or straps that get caught -- tight to the body with everyghing fastened would not be an issue.
I bought my pack because it was the smallest one I could find that had a ski-carry feature. I have had very few occaisions where I felt its thickness was pushing me too far forward, all on old chairs. (Olympic Lady at squaw springs to mind.)
Until this year, the only places that gave me trouble about the pack were Smugglers Notch and Middlebury Snow Bowl, both in Vermont. I was surprised when Stowe hassled me about it before Christmas (not having heard about this years incidents.) That day was after a thaw freeze cycle, so there were basically two black and two blue ways down, with minor variations. We were doing ten minute laps with no lift lines, so it got pretty annoying. Eventually I started leaving it most of the way off when we took the blue routes.
So I've thought about what I am going to do going forward, starting with what I keep in it and how often I use them. In the East, you are never that far from the lodge and there aren't many (official) places where hiking is needed, so I will probably give it up and deal with more-stuffed-than-I'd-like pockets. In the West, I'll probably deal with taking it off for each ride.