Win 7 64bit, Radeon HD 6850
tested in 2.72a & 2.72b
Short description of error
Volumetric Material appears wrong in Rendered Viewport Shading when World Background is black (0,0,0)
Exact steps for others to reproduce the error
Probably the World Background need to be black to reproduce this bug.
Possibly also a scene with black World Background Color must be saved as default startup file in advance.
Switch to Cycles Render Engine
Delete the default Cube and Lamp.
Add a UV Sphere, unwrapp it, add Diffuse Material, add UV mapped Image Texture to the Diffuse Color Input, set the Object to be Shaded Smooth.
Add an Ico Shere to same position as the UV Sphere is, scale the Ico Sphere slightly larger than the UV Sphere is, add a Volumetric Scatter Material, set the Ico to Shaded Smooth.
Add a Sun Lamp, turn Multiple Importance Sample on.
Switch the Viewport Shading to Rendered.
If the Volumetric Scatter Material appears wrong now somehow (like in the attachement / lower left image) go to the World Buttons
and change the Background Color to any brighter than black(0,0,0). If the Material appears correctly now it should stay like this even
if you change the Background Color to black again.