Creation of large graph(> 2.15 B nodes) seems to be broken:possible overflow somewhere

While creating a graph with 6B nodes and 12B edges, I noticed that 'numVertices' api returns incorrect result; 'numEdges' reports correct number. For few times(with different dataset > 2.5B nodes) I have also notices that numVertices is returned as -ive number; so I suspect that there is some overflow (may be we are using Int for some field?).

Here is some details of experiments I have done so far:
1. Input: numNodes=6101995593 ; noEdges=12163784626
Graph returns: numVertices=1807028297 ; numEdges=12163784626

2. Input : numNodes=2157586441 ; noEdges=2747322705
Graph Returns: numVertices=-2137380855 ; numEdges=2747322705

3. Input: numNodes=1725060105 ; noEdges=204176821
Graph: numVertices=1725060105 ; numEdges=2041768213

You can find the code to generate this bug here:

https://gist.github.com/npanj/92e949d86d08715bf4bf

Note: Nodes are labeled are 1...6B .