reStructuredText: Unable to render the second section when there's only two section

Summary

Unable to render the sub-section when there're only two sections in the Content.

###Steps to Reproduce

Use the following content:

#!python
Chapter 1 Title
=============

Section 1.1 Title
-----------------

###Expected Results
Only show "Chapter 1 Title"

###Actual Results
Show both "Chapter 1 Title" and "Section 1.1 Title"

###Workaround
Add another section into the content.
For instance:

#!python
Section 1.2 Title
-----------------

or 

Subsection 1.1.1 Title
~~~~~~~~~~~~~~~~~~~~~~

or 

Chapter 2 Title
=============