The maintenance required was just update version, and I did run that. Catalog sync did create duplicates again.
I reinstalled 5560, and copied the "Natur" catalog back as well (This is just a small catalog, so I had backed it all up, not only the catalog.pmdb).
Now it did require reintegration! After reintegration, all was back to normal. I quit PMP, and copied my catalog backup back once more, and this time it did not require reintegration. So apparently there are other files involved here, not only the catalog files. (caching? preference files?)
Hans-Jørgen