toctree numbering not shown on 'self' entries

[adamcharnock]

Problem

• tocktree entries which refer to self are not assigned a number when using :numbered:.

Procedure to reproduce the problem

# /index.rst

.. toctree::
    :maxdepth: 2
    :numbered:
    :titlesonly:

    self        # <-- Should be number 1, but doesn't get a number
    motivation  # <-- This is actually number one
    alternatives
    concerns
    implementation/index

Introduction
============

...

Screenshot:

No errors present in output, so omitting error logs. Will post output if requested.

Expected results

Numbering should start at first item in list. Mockup screenshot:

Reproducible project / your project

• Zipped /docs directory: docs.zip
• Project is adamcharnock/lightbus, commit ecbff9b7, browse docs at commit
• Rendered docs (at latest commit) can be seen at lightbus.org

Environment info

• OS: Mac, 10.12.5 (Sierra)
• Python version: 3.6.1
• Sphinx version: 1.6.3
• Extra tools: sphinx-autobuild==0.7.1, alabaster theme

[adamcharnock]

Also, #3142 seem to report a similar issue. However, I get the impression that the cause was different.