1908 2c Quebec to GB, then Germany, no postage due.

1908 2c Quebec to GB, then Germany, no postage due. #98 2c Quebec tied by Rock Island, Quebec duplex (SP 7) to London, GB, machine receiver SEP 16 8 30am, and redirected with London despatch (SEP 16 6 PM) to Pirnai, Germany bs (18 9 08). The cover shortpays the 5c UPU letter rate but was not charged postage due. A German seal “Kaiserl Deutscges Postamt Prina” in blue on the reverse. Message in German, perhaps explaining the cover was repaired with seal?