losing all results on diamond query

[cbizon]

If I query (V)-[p1]-(?gene)-[p2]-(C) where V and C are pinned, I get results
If I query (C)-[p1]-(?gene)-[p2]-(V) (same endpoints but swapped around) I get results

If I include both paths in the same query (2 gene nodes) I get 0 results.

---

This TRAPI query produces 0 results:

{
  "message": {
    "query_graph": {
      "edges": {
        "e00": {
          "subject": "n02",
          "object": "n01",
         "predicates":["biolink:degradation_increased_by", "biolink:is_substrate_of"]
        },
        "e01": {
          "subject": "n01",
          "object": "n00",
         "predicates":["biolink:activity_decreased_by","biolink:entity_negatively_regulated_by_entity"]
        },
       "e02": {
          "subject": "n00",
          "object": "n03",
          "predicates":["biolink:degradation_increased_by", "biolink:is_substrate_of"]
        },
        "e03": {
          "subject": "n03",
          "object": "n02",
          "predicates":["biolink:activity_decreased_by","biolink:entity_negatively_regulated_by_entity"]
        }
      },
      "nodes": {
        "n00": {
          "ids": ["PUBCHEM.COMPOUND:644019"],
          "categories": ["biolink:SmallMolecule"]
        },
        "n01": {
          "categories": ["biolink:Gene"]
        },
        "n02": {
          "ids": ["PUBCHEM.COMPOUND:3121"],
          "categories": ["biolink:SmallMolecule"]
        },
        "n03": {
          "categories": ["biolink:Gene"]
        },
      }
    }
  }
}

It is 2 independent paths connecting the same anchors.

If I run only one of those paths by dropping e02, e03, n03 then I get 8 results

{
  "message": {
    "query_graph": {
      "edges": {
        "e00": {
          "subject": "n02",
          "object": "n01",
         "predicates":["biolink:degradation_increased_by", "biolink:is_substrate_of"]
        },
        "e01": {
          "subject": "n01",
          "object": "n00",
         "predicates":["biolink:activity_decreased_by","biolink:entity_negatively_regulated_by_entity"]
        }
      },
      "nodes": {
        "n00": {
          "ids": ["PUBCHEM.COMPOUND:644019"],
          "categories": ["biolink:SmallMolecule"]
        },
        "n01": {
          "categories": ["biolink:Gene"]
        },
        "n02": {
          "ids": ["PUBCHEM.COMPOUND:3121"],
          "categories": ["biolink:SmallMolecule"]
        }
      }
    }
  }
}

If I instead delete the other two edges and gene node, I get 6 results

{
  "message": {
    "query_graph": {
      "edges": {
       "e02": {
          "subject": "n00",
          "object": "n03",
          "predicates":["biolink:degradation_increased_by", "biolink:is_substrate_of"]
        },
        "e03": {
          "subject": "n03",
          "object": "n02",
          "predicates":["biolink:activity_decreased_by","biolink:entity_negatively_regulated_by_entity"]
        }
      },
      "nodes": {
        "n00": {
          "ids": ["PUBCHEM.COMPOUND:644019"],
          "categories": ["biolink:SmallMolecule"]
        },
        "n02": {
          "ids": ["PUBCHEM.COMPOUND:3121"],
          "categories": ["biolink:SmallMolecule"]
        },
        "n03": {
          "categories": ["biolink:Gene"]
        },
      }
    }
  }
}

Because these two paths only intersect at bound nodes, I should get the cartesian join back (48 results)