Node matched too early in UNION on Enterprise

[DominicWuest]

I found a discrepancy when running two semantically equivalent queries against an empty database:

---

1:

RETURN 0 AS n1
	UNION
CALL {
  FOREACH ( n2 IN [] | FOREACH ( n3 IN [] | MERGE () ) )
} MATCH (y)
RETURN y AS n1
	UNION
CREATE ()
RETURN 0 AS n1

Produces:

╒═══╕
│n1 │
╞═══╡
│0  │
├───┤
│() │
└───┘

---

2:

FOREACH (n0 IN [] | FOREACH ( x IN [] | SET x = {} ) )
RETURN 0 AS n1
	UNION
CALL {
  FOREACH ( n2 IN [] | FOREACH ( n3 IN [] | MERGE () ) )
} MATCH (y)
RETURN y AS n1
	UNION
CREATE ()
RETURN 0 AS n1

Produces:

╒═══╕
│n1 │
╞═══╡
│0  │
└───┘

---

I believe the queries mentioned above are semantically equivalent and thus their result should be the same, since the first FOREACH is inconsequential, iterating over an empty list.

I encountered this issue when testing queries against the Neo4j 5.18.0 enterprise version in a Docker container running alpine v.3.

The query results are the same on Neo4j 5.13.0, but differ on Neo4j 5.14.0.
When testing the query against the community edition, the query results equal.
Additionally, when forcing the SLOTTED runtime, the results also equal.

It seems like the MATCH (y) clause mistakenly matches the nodes created in the last part of the UNION in the first query, as the returned node's labels match the ones of the node created there, if set.

Steps to reproduce

Run the aforementioned, semantically equivalent, queries against an empty database and observe that their results differ.

Expected behavior

The queries should result in the same behavior

Actual behavior

The query results differ