More graphs later and it now transpires that the apparent decrease does manifest itself BEFORE the CTR pumps are turned off.
Latest expanded scale plot shows the "dip" started at 8400kgs, so back to the drawing board for me.
Curiously some of my RHS colleagues had observed this apparent dip, others who look at the FMS figure minutes before the waypoint and record it as such, have not noticed.
I really must get outa the cockpit more..............................................
