Export contacts and choosing a relationship-based field does not work for all relationship types

I have reproduced the issue in the public sand box.

To reproduce:
1) Do a search on contacts, any criteria

2) In the list of actions, choose "Export Contacts"

3) On the next screen choose to "Select fields for export" then click "Continue"

4) Choose any field ( I chose sort name)

5) For the second field choose a relationship type that has the same name in both directions (I chose Spouse) Then choose field for the related contact. (I choose "sort name" of the spouse)

6) Click "Export"

In the resulting CSV file, some of the "sort name of spouse" fields are empty. It seems like the code only looked at the "a_b" part of the spouse relationship, not "b_a" This issue is impacting all relationship types where the relationship name is the same on both sides (or one label is blank)