Well, and the round is too short for the magazine, and frame. And, the system is designed for a straight walled case, while the 9mm is a tapered case. And, the original design wasn't necessarily .45 ACP hollow point friendly, let alone 9mm hollow point friendly. And, when you load the magazine, the top 9mm round sits at a different angle than the round immediately below it.
In observation, it takes so much, from some of the better engineers / gun smiths, to make a 9mm that run well, including both gun tweaks and a variate of magazine designs, to include different types of spacers and "ramps" included in the magazine itself, it does make one wonder if there isn't a better caliber / system for any kind of serious work.
Don't get me wrong, I love me some 9mm 1911s on the range and in a match. I've had an STI Trojan, S&W Performance Center 1911, and still own and competitively shoot a Les Baer Premier II 9mm and Cabot S100. I also have Wilson, Tripp, CMC, Dawson, Mecgar, and Metalform 9mm magazines.
Don't mean to be a downer, but I've been down this road for the long haul, and these are my strong opinions on the matter, based on a bit of experience. YMMV.