Union operator fails when resources are of same type but different profiles

[raleigh-g-thompson]

When applying the union operator to resources of the same type but different profiles, the union operator won't return values.

Failing Code

define "ConditionUnion":
  [ConditionProblemsHealthConcerns: "Dental Caries"] union [ConditionEncounterDiagnosis: "Dental Caries"]

[raleigh-g-thompson]

This may be related to issue #1577