Drag and droping files in a Document when there is already a main file

I have a doc in DM with 1 main file attached.
The drag and drop functions says: "Drag here files to add them as main files or attachment".
As there is already a main file, I expec the app. to add everything as attachment, but it dropped the main file.

I would expect a dialog box that ask if the main file should be replaced and if so, a selector to decide which of the uploaded doc shall be used.