Proxy URL behaviour for package list - trailing slash
In the System -> Advanced -> Miscellaneous settings, where you enter the proxy URL, if you have a trailing slash then the Update will work but not the package list. If you leave the trailing slash off then it works.
http://192.168.1.1/ will work for updates but not packages
http://192.168.1.1 will work for updates and packages.
This was found in 2.1-REALEASE (amd64)
Apparently no longer an issue due to input validation, the field accepts IP or FQDN only, not URL.