Gettext does not add substitutions to message catalogue

[TheRealMoeder]

Problem

Running gettext doesn't get messages within substitutions.

Procedure to reproduce the problem

sphinx-build -b gettext

example conf.py:

source_suffix = '.rst'
master_doc = 'index'
gettext_compact = False

index.rst:

Line 1

.. |testsub| replace:: test-substitution

Bla bla bla.

Testing |testsub|

Environment info

• OS: Debian 8.6.0 64 bit
• Python version: 2.7
• Sphinx version: 1.6.5.