Hey Korlon, thanks for the quick and kindly help, though the savegame you made up didn't work for me. Nevertheless I found a solution now to get rid of those iberian undercover-nazis. I simply starved them out. The garrison didn't sally but gave up without a fight, so the game didn't crash and Tarsos fell into the hands of Kingdom of Pontos (just to be given back to the Ptolemaians to annoy the Arche an work as a puffer between the grey superpower and me. The diadochii wars, shall they never end!)
Bovi, I hope this adds to your collection of weird and interesting minor bugs. Thank you too and also Olaf the Great moral support in the iberian case.