Yup, I think it's probably pretty common. I know that mine rapidly alternates between "sucking" (for lack of a better term) and forcefully pushing out during orgasm. Heck, I nearly put someone's eye out with a vibrator once. [:D]
If during orgasm you push out - hard enough to push the cock out of you - how do you *tries to put it delicately* not fart during the process.... or is that a by product of this intense orgasm/pushing experience as well?
It's a by product of intense orgasm. You know how during orgasm the walls clamp down? Well sometimes they clamp down hard enough to eject whatever was in there!
hehehe reminds me of this time my friend went to a swingers club and had guys coming in to "see" her third hand...one poor guy couldn't stay in for the life of him but like it was said earlier, size and gravity can help or hinder...