Cannot add listen: sls requisite

one.sls:

include:
  - two

ssh:
  service.running:
    - reload: true
    - listen:
      - sls: two

two.sls:

/trigger:
  file.absent: []

output:

local:
  Name: /trigger - Function: file.absent - Result: Clean Started: - 13:59:37.370668 Duration: 0.444 ms
  Name: ssh - Function: service.running - Result: Clean Started: - 13:59:38.037626 Duration: 46.214 ms
----------
          ID: listen_test.two
    Function: Listen_Error.Listen_Error
      Result: False
     Comment: Referenced state sls: test.two does not exist
     Changes:

Summary for local
------------
Succeeded: 2
Failed:    1
------------
Total states run:     3
Total run time:  46.658 ms

A require instead works fine.

Versions Report

Salt Version:
           Salt: 2018.3.4

Dependency Versions:
           cffi: Not Installed
       cherrypy: Not Installed
       dateutil: 2.6.1
      docker-py: Not Installed
          gitdb: 2.0.3
      gitpython: 2.1.8
          ioflo: Not Installed
         Jinja2: 2.10
        libgit2: 0.26.0
        libnacl: Not Installed
       M2Crypto: 0.32.0
           Mako: Not Installed
   msgpack-pure: Not Installed
 msgpack-python: 0.5.6
   mysql-python: Not Installed
      pycparser: Not Installed
       pycrypto: 2.6.1
   pycryptodome: Not Installed
         pygit2: 0.26.2
         Python: 3.6.7 (default, Oct 22 2018, 11:32:17)
   python-gnupg: 0.4.1
         PyYAML: 3.12
          PyZMQ: 16.0.2
           RAET: Not Installed
          smmap: 2.0.3
        timelib: Not Installed
        Tornado: 4.5.3
            ZMQ: 4.2.5

System Versions:
           dist: Ubuntu 18.04 bionic
         locale: ISO-8859-1
        machine: x86_64
        release: 4.15.0-50-generic
         system: Linux
        version: Ubuntu 18.04 bionic

Reproduce the issue with the one.sls and two.sls examples, comparing the listen sls requisite with the working require requisite. Trace the state requisite handling that produces the Listen_Error message, then add or update a regression test showing that the included two state resolves without an error.