Ah ha! I knew I wasn't going crazy! Months ago (in winter, here in CO), I was having some sort of work done on my Raptor at the dealer, and I mentioned to them that it seemed like my tailgate had popped open by itself 2 or 3 times previously, and asked them to take a look at it. There was no CSP notice at the time, and they couldn't find anything wrong, so I just chalked it up to my having pressed the tailgate release button accidentally with the keys still in my pocket, even though it seems very hard to do. Now that I know it wasn't me, I feel much better about the whole thing!