parallel discontinuation not working while using MD51, but it works with use of MD41

Discontinuation data is maintained in material master and BOM. The discontinuation date is in the past.

when I plan header material (MPS M0) with MD41, it works perfectly and demands fall on fallow up material but when I use MD51 It does not work, and demands fall on discontinued material.

follow up and discontinued materials have MRP type P3.

why is it so? Discontinuation not working for T code MD51 ( project level planning)

Please help