Janusgraph could not deal with correct path traversal results

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For confirmed bugs, please report:

- Version: 0.6.2
- Storage Backend: inmemory
- Mixed Index Backend: none
- Link to discussed bug: none
- Expected Behavior:
We construct the following scenario: x equals count nodes(A->B) path numbers, y equals count nodes(B->C) path numbers, z equals count(A->B->C) path numbers. Then z should equal x*y.
We generate graph schema and data based on random strings and values. We build the graph with 100 vertexes, 200 edges, 20 vertex labels, and 20 edge labels.
`g.V().id()` is used to get the node ids of the graph, then can use for loop to traverse all the nodes. Here is one of our examples executed.
1) `g.V(16416).repeat(out().simplePath()).until(hasId(4128)).path().size()` return 240
2) `g.V(4128).repeat(out().simplePath()).until(hasId(8224)).path().size()` return 557
3) `g.V(16416).repeat(out().simplePath()).until(hasId(4128)).repeat(out().simplePath()).until(hasId(8224)).path().size()`, should return 240*557.
- Current Behavior:
The query 3 return 83 != 240*557.
- Steps to Reproduce:
Although the randomness of the graph data generation process, we still find the problem after many attempts. Reproduce: Generate a large enough graph -> Get all node ids -> Count the number of paths for any two ids -> Multiply and compare following our strategy.

No source file, test, or deterministic graph fixture is identified. Start by reproducing the three traversals on JanusGraph 0.6.2 with the in-memory backend, using a fixed graph rather than random generation; done means confirming whether the combined path count should equal the product and documenting the cause or correction.

Written by the indexing model from the issue text.