Reasons a request would not be handled in Pretender

I have an xhr request in a custom authenticator using ember-simple-auth that doesn't get handled by pretender in tests. All of my other api calls get handled with no problems. No hooks for this request get called including unhandledRequest. The result is simply a 404 which causes tests to intermittently fail due to the 404 sometimes taking up to 3 seconds.

Any ideas about what might be causing this would be greatly appreciated.