Hello
Did you already researched the documentation about capacity reduction on repetitive manufacturing to check the expected system behavior on MFBF?
I suggest you to take a look on the following link:
http://help.sap.com/saphelp_erp60_sp/helpdata/en/8a/a592a74adc11d189740000e8322d00/frameset.htm
Here you can find the below information, which explains the system behavior in more detail:
Cap. Reduction with Reporting Point Backflushing
Since in the case of long execution times and several confirmation
points a single control point at the end of the production process is
not sufficient, repetitive manufacturing provides the function
"reporting point backflushing" (analogous to milestone confirmations).
The function involves backflushing of all materials that were withdrawn
and used between two reporting points. The material requirements are
reduced in real-time and the components are withdrawn in real-time.
The confirmation at reporting points has no effect on the reduction of
capacity requirements. These are only reduced with the final
confirmation."
BR
Caetano