Operattion dates

Hi

Iam using parallel sequence with branch operation 0 and return operation as 40 return operation.

There are 15 operations in main sequence

I have created 3 production orders each with quantity 1, for same material with same finish date.

For parallel sequence, last operation date comes different in 2 production orders and different in one operation.

When 2 production orders are re-schedule then in all production orders dates for parallel sequences come properly.

Please guide why dates in all 3 production orders are not coming same during creation mode.