As opposed to what others have said I hear that that is pretty normal. My daughter had that too and it actually helped a lot with the constant stuffy nose she had - she would only sleep well when nursing because the milk helped clear her nose. I was actually told to put some breatmilk in my daughter's nostrils to help with her nasal congestion. The stuffy nose is also pretty common in newborns, and, for us at least, had nothing to do with the milk coming up the nose.
If you haven't yet, try the football hold, it gives the baby a little more control over the milkflow.
Anyways, if it's a problem you should talk to your doctor.
Mine eventually grew out of it after a few months.