Relationships for contact subtypes can only be created in one direction

I found this bug on 4.4.5 and replicated on the 4.5 sandbox.

To replicate:

• Create a relationship type where one of the contact types is a contact subtype (e.g. Student of/Teacher of - Contact A is "Individual - Student" and Contact B is "Individual").
• If you create a relationship from a Student record, "Teacher Of" is not available as a relationship type - even though a student is also an individual.

The practical implication is that if you have two students in a student/teacher relationship - you can only create the relationship from the student's record and not the teacher's record.