The PMDG 737NG series incorporates a custom stabilizer trim gauge we had
to develop in order to make the trim work properly. Because the
stabilizer trim in FS9 runs at about 5 times the normal rate as the real
737's, it made the aircraft extremely hard to control with manual trim
inputs. We developed a custom gauge that slowed the speed to match that
of the real 737, but an unwanted side effect of this is the strange
animation behavior. Holding the trim for several seconds will allow
users to see that the stabilizer actually does move.