Mad Jock,
I'm well aware most airlines have good procedures in place to brief Cabin Crews what cabin moves may be allowed, however the OP's experience in that 8 passengers that had rear cabin zone seats swapped them to forward cabin zone seats is quite a trim change!
However, if this change is communicated and approved by the flight deck crew then all is well.
This Load Contoller aims to get the aircraft as near as possible to optimum trim by blocking seats if necessary and adjusting the Baggage and cargo loading to suit if possible. However, this work is sometime undone by check-in unblocking some of the seats to please passengers requests etc.
