Problem
The Mirror generates PReqs with incorrect start dates (usually, way before the availability date of the receipt it is supposed to match). The end dates are right, though.
Solution
The Planned Delivery Date of the Material in the receiving plant is likely 59, or 999 days. This causes the PReq start date to be wrong.
Either create a PIR with the right PDT, or if you can, and this is better: review the Planned Delivery Date of the material master.