Addon install copies zip-file instead of extracting

I have encountered a problem with version 9.1. I use the official way of installing an addon with a Zip-file through Prefenences >Install, but instead of extracting and installing in the \AppData\Roaming\Blender Foundation\Blender\2.91\scripts\addons directory, the complete Zip-file is copied one-on-one to this location.
The addons are renowend software like Traffic, Extreme PBR shaders and Spyderfy so I assume the content is correctly programmend. Is it possible that this phenomenon isdue to a maximum of installable addons?