Broken: official 2.6.9, own 0445454
Short description of error
Adding a Rereoute Node by Shift Mouse-click drag over existing Node Connection Places new Reroute node "out in space" anywhere about 200-800 Pixels away.
Usually above it. and actually depending on where on your existing Node Connection the Shift+Mouse "cut" happens. Near to the right (input) it miss-places way less than if cut left (output).
Exact steps for others to reproduce the error
Based on a (as simple as possible) attached .blend file with minimum amount of steps