graph.predecessors and graph.inEdges do not alway work

[JohnPool]

I noticed that (for a directed graph) graph.inEdges( node) and graph.predecessors( node) do not always work. In simple test examples they do work as expected, but in my code I have situations where in a part of the graph, say --> a --> b -->, graph.successors(a).length == 1, but graph.predecessors(b).length == 0 (and also graph.inEdges(b).length == 0).

The annoying thing is that this does not happen all the time (with the same, unmodified code).

Does anyone else have similar experiences?