pkgrepo.managed salt state does not update repo when proxy is deleted

Description of Issue/Question

Having this state:

saltstack:
  pkgrepo.managed:
    - humanname: SaltStack repo for RHEL/CentOS $releasever
    - baseurl: https://repo.saltstack.com/yum/redhat/$releasever/$basearch/latest
    - gpgcheck: 1
    - gpgkey: https://repo.saltstack.com/yum/redhat/$releasever/$basearch/latest/SALTSTACK-EL5-GPG-KEY.pub
    - proxy: _none_

After removal of proxy attribute, highstate does not change provisioned repo file.

Steps to Reproduce Issue

When I add proxy: none attribute to state, it will be reflected. When I remove it (I expect that proxy config will be removed from repo file), it does not trigger any change on minion.

Versions Report

(Provided by running salt --versions-report. Please also mention any differences in master/minion versions.)

cat /etc/redhat-release 
CentOS Linux release 7.2.1511 (Core)

salt-call --versions-report
Salt Version:
           Salt: 2016.3.2

Dependency Versions:
           cffi: Not Installed
       cherrypy: Not Installed
       dateutil: Not Installed
          gitdb: Not Installed
      gitpython: Not Installed
          ioflo: Not Installed
         Jinja2: 2.7.2
        libgit2: Not Installed
        libnacl: Not Installed
       M2Crypto: 0.21.1
           Mako: Not Installed
   msgpack-pure: Not Installed
 msgpack-python: 0.4.8
   mysql-python: Not Installed
      pycparser: Not Installed
       pycrypto: 2.6.1
         pygit2: Not Installed
         Python: 2.7.5 (default, Aug 18 2016, 15:58:25)
   python-gnupg: Not Installed
         PyYAML: 3.11
          PyZMQ: 15.3.0
           RAET: Not Installed
          smmap: Not Installed
        timelib: Not Installed
        Tornado: 4.2.1
            ZMQ: 4.1.4

System Versions:
           dist: centos 7.2.1511 Core
        machine: x86_64
        release: 3.10.0-327.28.2.el7.x86_64
         system: Linux
        version: CentOS Linux 7.2.1511 Core

Start with the pkgrepo.managed state behavior and reproduce the issue using the provided state, first adding and then removing proxy: none. Inspect the generated repository file and highstate result; done means removing the proxy setting from the state also removes it from the provisioned repo file.