HAH~ I never thought a small piece of meat could stall so long UNTIL I did it the other day. I had believe it or not a 5lb "packer" from the grocery store here and it took about 12 hours, by this time it was 11 pm and I took it off and the internal temp was still only like 180 and only some parts were probing we'll and the point on the brisket was way way undercooked still. Every piece of meat is different, so I'm not surprised you had such a long stall. Whatever you do, don't rush it (Even if your hungry.) I wasted 11 hours of smoking for a undercooked brisket :(
**Edit** And yes, I had 3 thermometers, so the heat in the smoker was spot on at 250.