Comment 4 for bug 1762673

The same behaviour persists on 2.6, proxy is not shutting down completely, and it's still working as a proxy even when disabled explicitly in the settings:

ubuntu@OrangeBox84 ~ » maas admin maas get-config name=enable_http_proxy 1 ↵
Success.
Machine-readable output follows:
true

ubuntu@OrangeBox84 ~ » sudo service maas-proxy status | head -n3 130 ↵
● maas-proxy.service - MAAS Proxy
   Loaded: loaded (/lib/systemd/system/maas-proxy.service; enabled; vendor preset: enabled)
   Active: active (running) since Tue 2019-09-03 08:29:47 UTC; 1 weeks 1 days ago

ubuntu@OrangeBox84 ~ »

ubuntu@OrangeBox84 ~ » maas admin maas set-config name=enable_http_proxy value=false
Success.
Machine-readable output follows:
OK

ubuntu@OrangeBox84 ~ » sudo service maas-proxy status | head -3
● maas-proxy.service - MAAS Proxy
   Loaded: loaded (/lib/systemd/system/maas-proxy.service; enabled; vendor preset: enabled)
   Active: active (running) since Tue 2019-09-03 08:29:47 UTC; 1 weeks 1 days ago

...but proxy is still running:

ubuntu@OrangeBox84 ~ » http HEAD localhost:8000
HTTP/1.1 400 Bad Request
Connection: close
Content-Language: en
Content-Length: 3525
Content-Type: text/html;charset=utf-8
Date: Wed, 11 Sep 2019 17:34:35 GMT
Mime-Version: 1.0
Server: squid/3.5.27
Vary: Accept-Language
Via: 1.1 OrangeBox84 (squid/3.5.27)
X-Cache: MISS from OrangeBox84
X-Cache-Lookup: NONE from OrangeBox84:8000
X-Squid-Error: ERR_INVALID_URL 0

ubuntu@OrangeBox84 ~ » ip -4 a s br0
5: br0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc noqueue state UP group default qlen 1000
    inet 172.27.84.1/23 brd 172.27.85.255 scope global br0
       valid_lft forever preferred_lft forever

ubuntu@OrangeBox84 ~ » ssh ubuntu@172.27.85.4
Welcome to Ubuntu 18.04.2 LTS (GNU/Linux 4.15.0-58-generic x86_64)
ubuntu@juju-1:~$ http_proxy=172.27.84.1:8000 https_proxy=172.27.84.1:8000 curl -I https://ubuntu.com
HTTP/1.1 200 Connection established

HTTP/1.1 200 OK
Date: Wed, 11 Sep 2019 17:43:07 GMT
Server: nginx/1.15.8
Strict-Transport-Security: max-age=15768000
Content-Type: text/html; charset=utf-8
Content-Length: 74959
Vary: Accept-Encoding
X-View-Name: canonicalwebteam.templatefinder.templatefinder.template_finder
X-VCS-Revision: 1568214796-add60a1
X-Request-Id: bec6731de1a039b2a937397da8a32ecb
Age: 13
X-Cache: HIT from nuno.canonical.com
X-Cache-Lookup: HIT from nuno.canonical.com:80
Via: 1.1 nuno.canonical.com (squid/3.5.12)

ubuntu@OrangeBox84 ~ » sudo tail /var/log/maas/proxy/access.log -n1 1 ↵
1568223800.906 222 172.27.85.4 TCP_TUNNEL/200 3656 CONNECT ubuntu.com:443 - HIER_DIRECT/91.189.89.110 -