Disappearing custom grains under Salt

Output

saltmaster@salt-w1:~/master/config/local_base_files/_grains$ salt 'keymaster.tproa.net' saltutil.sync_grains
keymaster.tproa.net:
    - grains.tproa_os_path
saltmaster@salt-w1:~/master/config/local_base_files/_grains$ salt 'keymaster.tproa.net' grains.item tproa_os_path
keymaster.tproa.net:
    ----------
    tproa_os_path:
        os.debian.jessie
saltmaster@salt-w1:~/master/config/local_base_files/_grains$ salt 'keymaster.tproa.net' state.highstate > /dev/null
saltmaster@salt-w1:~/master/config/local_base_files/_grains$ echo $?
0
saltmaster@salt-w1:~/master/config/local_base_files/_grains$ salt 'keymaster.tproa.net' grains.item tproa_os_path
keymaster.tproa.net:
    ----------
    tproa_os_path:
saltmaster@salt-w1:~/master/config/local_base_files/_grains$

Salt Master Versions

saltmaster@salt-w1:~$ salt --versions
           Salt: 2015.5.2
         Python: 2.7.9 (default, Mar  1 2015, 12:57:24)
         Jinja2: 2.7.3
       M2Crypto: 0.22
 msgpack-python: 0.4.6
   msgpack-pure: Not Installed
       pycrypto: 2.6.1
        libnacl: Not Installed
         PyYAML: 3.11
          ioflo: Not Installed
          PyZMQ: 14.7.0
           RAET: Not Installed
            ZMQ: 4.0.5
           Mako: Not Installed

Salt Minion Versions

root@keymaster:/var/log/salt# salt-minion --versions
                  Salt: 2015.5.2
                Python: 2.7.9 (default, Mar  1 2015, 12:57:24)
                Jinja2: 2.7.3
              M2Crypto: 0.21.1
        msgpack-python: 0.4.2
          msgpack-pure: Not Installed
              pycrypto: 2.6.1
               libnacl: Not Installed
                PyYAML: 3.11
                 ioflo: Not Installed
                 PyZMQ: 14.4.0
                  RAET: Not Installed
                   ZMQ: 4.0.5
                  Mako: Not Installed
 Debian source package: 2015.5.2+ds-1