Something to be aware of that may or may not affect the patch I'm preparing:

One reason that Sphinx seems able to render some of the more complicated function signatures is that it has logic to bail and print the parameter list verbatim from the reST file whenever its record-keeping logic becomes internally inconsistent:

except IndexError:
    # if there are too few or too many elements on the stack, just give up
    # and treat the whole argument list as one argument, discarding the
    # already partially populated paramlist node

https://bitbucket.org/birkenfeld/sphinx/src/1f3a2749df39/sphinx/domains/python.py#cl-74

This seems to come into play, for example, when rendering--

sorted(iterable[, key][, reverse])

http://docs.python.org/dev/library/functions.html#sorted