Intervention email crashes

Heres the data dump, I was emailing username and password that might have triggered it?
;;;;;;;;;;;;;;;;;;;;;
 Server Error

An internal server error has occurred. This most likely means that you have found a bug in SchoolTool. Please report it on the issue tracker.
Exception

DuplicateRelationship:

Traceback

File "/usr/lib/python2.7/dist-packages/zope/publisher/publish.py", line 132, in publish
  result = publication.callObject(request, obj)
File "/usr/lib/python2.7/dist-packages/zope/app/publication/zopepublication.py", line 205, in callObject
  return mapply(ob, request.getPositionalArguments(), request)
File "/usr/lib/python2.7/dist-packages/zope/publisher/publish.py", line 107, in mapply
  return debug_call(obj, args)
Extra information: <schooltool.skin.flourish.zcml_content.FlourishInterventionMessageAddView_addMessage.html object at 0xaafc04cc>
File "/usr/lib/python2.7/dist-packages/zope/publisher/publish.py", line 113, in debug_call
  return obj(*args)
File "/usr/lib/python2.7/dist-packages/schooltool/skin/flourish/page.py", line 70, in __call__
  self.update()
File "/usr/lib/python2.7/dist-packages/schooltool/skin/flourish/form.py", line 72, in update
  super(AddForm, self).update()
File "/usr/lib/python2.7/dist-packages/schooltool/skin/flourish/form.py", line 55, in update
  super(Form, self).update()
File "/usr/lib/python2.7/dist-packages/z3c/form/form.py", line 211, in update
  self.actions.execute()
File "/usr/lib/python2.7/dist-packages/z3c/form/action.py", line 99, in execute
  result = handler()
File "/usr/lib/python2.7/dist-packages/z3c/form/button.py", line 315, in __call__
  return handler(self.form, self.action)
File "/usr/lib/python2.7/dist-packages/z3c/form/button.py", line 170, in __call__
  return self.func(form, action)
File "/usr/lib/python2.7/dist-packages/schooltool/intervention/browser/intervention.py", line 1118, in handleAdd
  obj = self.createAndAdd(data)
File "/usr/lib/python2.7/dist-packages/z3c/form/form.py", line 248, in createAndAdd
  self.add(obj)
File "/usr/lib/python2.7/dist-packages/schooltool/intervention/browser/intervention.py", line 1156, in add
  message.recipients.add(IContact(recipient))
File "/usr/lib/python2.7/dist-packages/schooltool/relationship/relationship.py", line 634, in add
  (other, self.other_role), extra_info)
File "/usr/lib/python2.7/dist-packages/schooltool/relationship/relationship.py", line 80, in relate
  raise DuplicateRelationship

Modules

schooltool 2.8.5 (/usr/lib/python2.7/dist-packages)

schooltool.cando 2.8.2 (/usr/lib/python2.7/dist-packages)

schooltool.gradebook 2.8.4.1 (/usr/lib/python2.7/dist-packages)

schooltool.intervention 2.7.0 (/usr/lib/python2.7/dist-packages)

schooltool.lyceum.journal 2.8.2.1 (/usr/lib/python2.7/dist-packages)
Runtime

Python 2.7.6 (default, Jun 22 2015, 18:00:18) [GCC 4.8.2]

Linux ubuntu 3.13.0-95-generic #142-Ubuntu SMP Fri Aug 12 17:05:16 UTC 2016 i686 i686