Yeah it occasionally does but I can forgive that minor problem. from what I can see the peg only pops out when the arms are handled roughly and are being pulled in a way that forces them to pop out.
the fact that they're aesthetically pleasing and leave the forearms smooth and unmarred by big black wheels and also not just hanging off the back like you're not supposed to see it - makes it a winning design formula in my eyes. the only thing holding it back from perfection is a way to clip the arms and shoulders together so that they don't pop out unintentionally.