Autosummary generates overly-long summaries if first line doesn't end with a period
If a function/module/etc has a docstring that looks like this:
I am the summary ...but it didn't end with a period, and there IS a sentence that ends with a period later, so this whole thing will become the summary.
...then the entire thing will get included as the "summary". This was introduced by the fix to issue 943 - https://bitbucket.org/birkenfeld/sphinx/issue/943/autosummary-doesnt-always-get-first - which attempted to detect situations where the first sentence of a docstring spanned multiple lines.
Unfortunately, it doesn't include detection for situations like the one above, where blank lines are used to indicate the end of the "summary".
I have a patch, which detects blank lines, and will submit a pull request shortly...