salt: Cannot `require_in` an entire SLS

Salt:

                      Salt: 2014.7.2
                    Python: 2.7.9 (default, Apr  2 2015, 15:33:21)
                    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: 14.4.1
                      RAET: Not Installed
                       ZMQ: 4.0.5
                      Mako: 1.0.0
     Debian source package: 2014.7.2+ds-1utopic2

OS: Ubuntu 15.04, using 14.10 Salt packages

When declaring a requisite like

include:
  - apache.modules
[…]
  - require_in:
    - sls: apache.modules

the state will fail with a message like this:

    Cannot extend ID 'apache.modules' in 'base:config'. It is not part of the high state.
This is likely due to a missing include statement or an incorrectly typed ID.
Ensure that a state with an ID of 'apache.modules' is available
in environment 'base' and to SLS 'config'

Using just apache as include/requisite, everything will work just fine, but once a “sub-SLS” is declared, it will fail as described above.

EDIT: A minimal working example: foo/bar.sls

some-test-stuff:
  test.succeed_with_changes

config.sls

include:
  - foo.bar

another-test-state:
  test.succeed_with_changes:
    - require_in:
      - sls: foo.bar

Result:

salt-call state.sls config
[WARNING ] Although 'dmidecode' was found in path, the current user cannot execute it. Grains output might not be accurate.
[WARNING ] Although 'dmidecode' was found in path, the current user cannot execute it. Grains output might not be accurate.
[INFO    ] Loading fresh modules for state activity
[INFO    ] Fetching file from saltenv 'base', ** done ** 'config.sls'
[INFO    ] Fetching file from saltenv 'base', ** skipped ** latest already in cache 'salt://foo/bar.sls'
local:
    Data failed to compile:
----------
    Cannot extend ID 'foo.bar' in 'base:config'. It is not part of the high state.
This is likely due to a missing include statement or an incorrectly typed ID.
Ensure that a state with an ID of 'foo.bar' is available
in environment 'base' and to SLS 'config'
root@moria:~/salt-teststates# cat config.sls 
include:
  - foo.bar

another-test-state:
  test.succeed_with_changes:
    - require_in:
      - sls: foo.bar