After inputting two nodes (ids were generated with 0 and 1) with 1 edge into a directed graph, I believe that this line gave my only edge a source node id of 2, when there was no source node id of 2. This generated invalid graphml.

[c-lombardi]

QuickGraph/3.0/sources/QuickGraph/Algorithms/AlgorithmExtensions.cs

Line 118 in 2f92ed6

ids[e] = id = ids.Count.ToString();