[graph-tool] Weighted Clustering

I have an edge property for weight. The weight for each edge is one integer between 1 and 4. The unweighted global clustering coefficient is about 0.45. The weighted global clustering coefficient is -0.61. Are negative values in the range? Additionally, if I filter on edge weight and calculate the weighted clustering I get values > 1.0. If all weights are 3, for example, would we not expect the same coefficient for weighted and unweighted. The unweighted coefficient for the above example is reasonable. The graph has 22K vertices and 3.7M nodes. I suspect this is something that I have overlook as I am new to graph-tool. Thank you.