Reading through issue1692335 provides a sense of the concerns surrounding the patches they applied to the 3.x branches.  Attempting to backport those patches to the 2.7 branch involves non-trivial risk, magnified by the now numerous differences between those branches.

If we had a reasonable workaround to use in 2.7, that would simplify things.

Example workaround that produces behavior in 2.7.12 very like what's observed when using 3.5 or 3.6:
        try:
            subprocess.check_call(['dcon'], stdout=fh, stderr=fh)
        except subprocess.CalledProcessError as cpe:
            raise Exception(str(cpe))