In Administration -> Server -> HTTP -> Web proxy the field "Proxy bypass hosts" gives the following default value "localhost, 127.0.0.1" and this as a description "Comma separated list of (partial) hostnames or IPs that should bypass proxy (e.g., 192.168., .mydomain.com)"

However if you try to add a host or IP that should be bypassed by the proxy following the default pattern, that is "coma-space-host" the pattern won't be matched because the white spaces are not trimmed on the comparison.

The request (made with the Moodle curl lib in my case) is not recognised as an exception and will use the proxy anyway and fail.