Cannot edit properties after overwriting file in a document library

I am (programmatically) overwriting a file in a document library after which none of the metadata fields can be edited either programmatically or manually:

Edit Properties -> change something -> Save

There is no error, just none of the metadata fields will actually update. To overwrite the file, I am using copy.asmx webservice. I get the same result when overwriting via REST, or just doing a plain http PUT. I also tried list.asmx webservice to update metadata. As long as I don't overwrite a file, everything works great.

This is Sharepoint 2010. Versioning is off, checkout is not required. "Overwriting" means there is an existing file, previously uploaded manually or with copyservice and the new file has the same name.

Has anybody seen this behavior? (or managed to get a sharepoint document library file into a similar state).

Thanks, RL