Obtaining negative scores on the EdgeBetweennessCentrality metric

[AdrianSeguraOrtiz]

 * JGraphT version: 1.5.1
 * Java version (java -version)/platform:  11

Issue
I am getting negative values in the EdgeBetweennessCentrality metric for some of my graphs. I don't know if this is really an implementation error or if a negative value is possible for this metric. In case it is not a bug, what interpretation should I give to it?

Steps to reproduce (small coding example)
graph.txt

// Load graph as SimpleDirectedWeightedGraph<Integer, DefaultWeightedEdge>
EdgeBetweennessCentrality<Integer, DefaultWeightedEdge> evaluator = new EdgeBetweennessCentrality<>(graph);
double[] scores = evaluator.getScores().values().stream().mapToDouble(Double::doubleValue).toArray();