Supplier Release Scheduling & MRP Messages

Hi - There is an inconsistency in the way system marks 'Y' for processed messages when R34400 (Generate Supplier Schedule) program is run. Depending upon the Frozen days and Releasable days, the schedule is as expected whereas the corresponding MRP messages are not marked with 'Y' consistently. Quantities are cumulated and one message is marked with a 'Y' while the others are not. The system allows processing the unmarked ones, which results in the creating orders in both Supplier schedule and an MRP message. Is there a logic behind marking 'Y'? Kindly advise

Example:

Assume order messages are generated by MRP for 02/15/2019, 02/22/2019, and 03/01/2019 with 100 quantities each. The system marks 'Y' only for the MRP message dated 03/01/2019 and leaves the messages for  02/15/2019 and 02/22/2019 blank. Quantities in supplier schedule are for 03/01/2019 - 300 quantities (Based on days setup n F4321). On testing further, the unmarked messages are getting processed in P3411 to create new orders.