@gertjan
There is an underlying misconception why Update Accelerator integrates into Squid managed by ipFire.
After all, pfSense does it too.
In the pfSense documentation on Squid there is a section just dedicated to Windows Update with the patterns recommended by Squid.
So we are not violating Windows functionality.
What Update Accelerator does is to use Squid to download the update and then save the files in a separate folder.
When Squid intercepts a new download, instead of looking in the cache, it fetches the file in this other folder.
Same thing for the other updates that are not from Microsoft.
I am not part of the development team, I just find that this is what is described in the documentation and that U.A. is activated in the Squid configuration page.