If you use a support carriage downstream of a Carriage Adapter, it will make blocks upstream of the carriage adapter move too.
Simplest setup to see this would be
[CM]
[FC]
[FC][St][St]
[FC]
[CA]
[SC]
[St]
(CM=carriage motor; FC=frame carriage; St=stone; CA=carriage adapter; SC=support carriage)
Intuitively, the 2nd stone in the 3rd row shouldn't move, but it does.