Issue 29723 is a follow up issue to this one, where these changes revealed some latent defects in how sys.path[0] was being initialised in general for directory and zipfile execution (those defects mean the change committed here adds an extra directory to sys.path when *not* running in isolated mode).

Paul, are you in a position to rebuild 3.6 with the changes from https://github.com/python/cpython/pull/575 and indicate whether or not that still fixes the original problem?