As discussed in #224, sphinx 1.4 has caused two new warnings to appear. One was fixed in #224, but this one remains:

WARNING: while setting up extension astropy_helpers.sphinx.ext.autodoc_enhancements: directive 'autoattribute' is already registered, it will be overridden

And from #224 (comment):

The first warning is coming from this https://github.com/astropy/astropy-helpers/blob/master/astropy_helpers/sphinx/ext/autodoc_enhancements.py#L75

I tried to catch the warning there and ignore it, but it didn't work. Getting the bug workaround into upstream sphinx may be the best long term solution.