Basically this bug is about the fact, that update-manager doesn't realize that the repository that's provided by our apt-proxy is a valid repository for updating.
The part, where it only re-adds main is probably a consequence of that.
I'm attaching my sources.list (which is pretty standard, except that archive.ubuntu.com is replace by 192.168.1.17:8090, where our local apt-proxy is running).
The fact that "real" third-party repositories are disabled is no problem at all.
I don't have any such line in my sources.list.
Basically this bug is about the fact, that update-manager doesn't realize that the repository that's provided by our apt-proxy is a valid repository for updating.
The part, where it only re-adds main is probably a consequence of that.
I'm attaching my sources.list (which is pretty standard, except that archive.ubuntu.com is replace by 192.168.1.17:8090, where our local apt-proxy is running).
The fact that "real" third-party repositories are disabled is no problem at all.