Hello
The planned order was not created to cover the sales order requirement, it was created to cover a dependent requirement that is under the sales order special stock. It means that the sales order delivery date is not relevant for this calculation.
From the MD04 screenshot we can observe that the dependent requirement date is 18.05.2015. System tried to create the planned order with this date as the basic finish date, however, the start date would be in the past (considering the in-house production time). System then automatically changed to forward scheduling and calculated the basic finish date.
BR
Caetano