Why won't milk flow stop when pumping?

There's one particular "stream" of milk that won't stop coming out. It turns a 20 minute pumping into a 45 minute pumping in order to empty that part of the breast. The rest of my breasts can be bone dry for 20 minutes or more, but that stream keeps shooting out. I've tried compressions and massaging that area, but nothing speeds it up. Any idea what is causing this and what I can do about it?