I find with 9.3.103.5 that the two instances scroll together if “scroll with other programs” is enabled. But if “scroll with other programs” is not enabled, the two instances do not scroll together.
So it surprises me that two instances of 9.2 do not scroll together when scroll with other programs is enabled. Unless scroll with other programs was not enabled in both instances. (If it is not enabled, and you open two instances, then turn on scroll with other programs in one instance, the other instance will still have it turned off.)