I experimented for the first time adding a runway in the general location of KPAE (Paine Field).
Strangly, miles away, just off shore to the southwest, the land elevation jumped up to form a narrow wall about 500 feet high and about the same amount long - in line with the runway. I deleted the runway but the terrain elevation did not return to normal (although the the terrain in the immediate vicinity of the runway DID return to normal).
Is there a way to reset it or should I just reload everything?