Ooh, I’ve had a couple pop-outs over the years. It happened with larger doses and when I was extensively re-using syringes, in particular. I think it’s like trying to fill up a water balloon. And you and me are the water balloons :-). i.e. start putting liquid in, but the more you put in the more the balloon is gonna push back.
I still occasionally get some coming back out, after removing the syringe. I think it depends somewhat on injection technique.