you probably have to operate on the sub plans independently. What I suspect is happening is that when you copy the data back into the master it is doing precisely that - copying it into the open plan which is the master plan. If you want to copy the data into the sub plans you need to have them open and copy into them.
It maybe possible to do this from within the master by copying only the data for each sub plan into the specific "section" (i.e. plan) in the master document.