Ubuntu, 64-bit, Nvidia graphics card (not sure of exact version)
Short description of error
If you extrude a new vertex with ctrl+click or 'e', then ctrl+right click on another vertex (which should select the shortest path between the vertices), the wrong vertex will often be chosen as the end of the path.
Exact steps for others to reproduce the error
Open the attached .blend file, switch to edit mode, select only the top-left vertex, ctrl+click somewhere on the left to create a fifth vertex, ctrl+right click on the vertex on the bottom-left of the quad. This should select the shortest path from the new vertex to the bottom-left vertex, but instead it selects a path to the bottom-right vertex. This is reproducible every time, as long as nothing is done in between any of the steps.