I disabled showing ZIP archives as folders by entering this *.reg info:
[-HKEY_CLASSES_ROOT\CompressedFolder\CLSID]
[-HKEY_CLASSES_ROOT\SystemFileAssociations\.zip\CLSID]
This works in Windows Explorer: double clicking a ZIP file opens the 7Zip program. But in DOpus it still causes the archive to be opened as a folder (even after restarting DOpus after the registry change).
Is this a bug, or should I disable compressed folders differently? To repeat: ZIP archives are now handled as desired under Windows Explorer.