**System Information**
WIndows 10,AMD 5450
**Blender Version**
2.77,Hash: 22a2853
**Short description of error**
The speed pass at the render layers is called "Vector",But in the node editor and the vector blur is called "Speed",Speed is wrong as it is not scalar quantity instead it should be called "Velocity" to be real vector quantity and it should also be the same at the render layers panel.
I don't know if that can be considered a bug,but I know that some people got confused multiple times because of this.