System Information
Operating system : Windows 7 Enterprise + service pack 1
Graphics card : NVIDIA GeForce GTX 480

Blender Version
Broken: v2.72 (hash : eb464ee if it is useful)

Short description of error
When rendering the velocity vector in Cycles, some objects (in my case, the ground) that don't move aren't black, as they are supposed to be. When rendered with Blender Render, the problem disappears.

Exact steps for others to reproduce the error
In the blend file, run the animation once.
Select Cycles, render and see the velocity in the viewer node.
Do the same thing while selecting the Blender Render.

I added the blend file and two images for clarity.

Rendered with Blender Render.

Rendered with Cycles.