Why?

What is fucking test 31?? Does anybody know?
I use Dijkstra on residue network from several sources to sink.

For every edge (u, v):
1) if flow < capacity then cost = 0
2) if flow > 0 then graph contains back edge (v, u) with cost = 0.

Dijkstra initialize sources (nodes of the graph, where excess of flow > 0) with cost = 0. We find shortest path from one of sources to the sink. Then we make changes with edges used in shortest path and out results.

What's wrong??