Striche statt Stempel auf polnischen Marken?!

Sieht nach Entwertung durch den Briefträger aus, sowas gibt es doch bis heute...

Hello
Sorry if i answer in english. I can't be sure of course, but seems to me reasonable they've been used to cancel the stamps in place of postmarks.
Why the postmarks have not been used it's another matter. They could be stamps not cancelled in the shipment office and cancelled by pen i.e. before the delivery (even by the postman).
But i've received no more than two-three weeks ago a letter with the same kind of cancellation, so it's something which can happen...