I suspect that this has to do with Xenforo, because I have run into the same problem on another forum which uses it, too, and then today on a third forum which also uses Xenforo. Coincidence? I don't think so!
I have the problem too, but it's a Xenforo and Safari(?) thing - not just MacRumors. Only see it on my Mac - never iOS.
In a backroom discussion on this a couple of the mods noticed it on other XF sites also.