Thanks. Yeah, having read more, it seems there's an 'odd' rule with international to domestic connections and customs requirements at OSL. I guess there aren't too many international-international connections there when you think about it, so I can see why people may be confused.
ps. I assume you didn't just run to the gate but had to go via the transfer area near gate 42?
Yeah gates 42 and 44 ring a bell. Up the steps from the airbridge, through a door marked "International connections" with a sleepy-looking security person who seemed surprised to see me, down the stairs and straight onto the next aircraft.