Hayo,
I agree there are two issues. From what I saw happening, there is something in PM. The files were never flagged as read only in Windows. I checked by using file explorer and displaying the file attributes, and also by going back to the old DOS prompt and using the attrib command. Neither showed any read only files.
PM also got to the point where I had 12 files marked read only in PM, but not Windows. I could not do anything with those files - the green dot went away, PM would not copy or move them, and PM would not delete them. In Windows, I was able to move them to another folder, but the catalog did not release them. When I added them back in, I had an image count of 12 more images than I have.
I then tried to delete the catalog through Manage Catalog, and that ran for about 15 minutes (7100 images) and still hadn't completed. I used Windows to delete the PM catalog folder, let PM recreate the folder, used Manage Catalogs to forget the catalog, and re-created it. The loading and indexing went fine.
There is some condition, and it may be a timing issue, where PM thinks the file is read only. I say this based on how I saw PM behaving. Before it locked those 12 files up, I would get a read only condition in the IPTC panel, use the navigation arrows to move either forward one image or back one image (both worked) and then return to the image that gave the read only notification, and upon return, the read only was gone and I could edit the IPTC panel.
Hope this helps!
-- kc