All images marked as changed when importing back from second catalog

Hello,

when I export part of my images into another catalog to edit them on another machine and later want to import them back into the main catalog, every image is marked as changed, even untouched images. Vitual copies seem to be the exception.

Even if I dont open the new catalog, i.e. export and immediately import them back.

I tried after deleting the Lightroom Settings Folder in %APPDATA% like the Support suggested. I tried with a new catalog with just some example images. The problem occurs on two machines.

Is it caused by some setting?