Sorry...but I found this is hard to believe Why?
It's a "SNUGFIT" between the lens and body. You really have to push the release button deep down. Then the lens needs to rotate with slight pressure. Both steps need to happen at the same time for the lens to be released. And you asking me WHY?
In this case, I would look for product quality issues or operator errors, not "design flaw"
1. Yes I am aware that "it's a SNUGFIT between the lens and body".
2. Yes, I asked you "why" bcoz the OP CLEARLY stated: "I must've hit it accidentally and then, when zooming, rotated the lens off the camera. I tested it with my 16-35 (that I've shot with for years with no trouble) and the zoom ring is farther down the barrel, so it doesn't get bumped. Is this a design flaw with the new 24-70 or am I doing something different from every other photog out there?
... no where did he blame Canon for design flaw.
I see that you did, later on, clarify that you are "more leanning to product quality issues
", but your original post was just a one line asking that you find it "hard to believe
", hence my earlier question Why?
Having said that, the OP came to CR to seek assistance and the least we can do is give him the benefit of doubt that something could have gone wrong with the mount, but surprisingly, several people (including those who are generally helpful) in this thread have just jumped on him without giving him the benefit of doubt ... what if something had genuinely gone wrong with the release button which did not require it to "push the release button deep down"?
I know no one directly blamed the OP that he might sue Canon for this but some of the posts seem to imply that ... imagine coming to a forum asking a question (to seek assistance) but only to hear insinuations that you might be a creep trying to "cash in" on an unfortunate accident ... that's a bit harsh.