ExtensionManager: Overwriting existing extensions with older versions without warning
The ExtensionManager should not install extensions without prior warning.
The ExtensionManager is fetching dependencies if needed to install an extension. In this case ExtensionManager is fetching older versions and thus overwriting existing extensions.
This can lead to fatal errors, breaking the whole backend.
Then it is only possible to remove all cache files by hand and removing the extension entry in LocalConfiguration.php.