At least, the arrow doesn't get drawn.
Once again, in my application: https://github.com/moschlar/SAUCE/blob/develop/sauce/model/user.py#L167 , you can see that there is
ForeignKey('students.id') which itself is
id = Column(Integer, ForeignKey('users.id'), primary_key=True).
If I change the ForeignKey in the secondary mapping table to
ForeignKey('users.id'), the arrow gets drawn (but to the User entity of course, so I suppose it comes from the inheritance and uncommon ForeignKey placement.
Of couse, I can just add the two arrows in the dot-file, but maybe you'll want to have a look at it! ;)