TYPO3 Core

Hi,

I suggest this is a bug, because before upgrading from 4.7 to 6 the same configuration worked.
The saveAction from the ConfigurationController of the extensionmanager throws the following Exception:
An argument "extension" does not exist for this request.

I checked the initialisation of the ext_conf_template.txt files but there is no parameter to set like "extension".
The form in the backend has a hidden input field which commits a variable named "extensionKey".

Here is my configuration:
# cat=module/enable; type=user[EXT:stag/Classes/Install/Installation.php:VENDOR\Extname\Install\Installation->init]; label=Installation Process:Refreshes all actions for the stag installation
excecuteActions=1

The relating class method does nothing. It is extending no other methods.
I can't find any similar core-classes to explain myself the process. So I assume this is missing or mixed up with extensionKey in the core form-template?