Trying to animate the intensity setting in the textures panel for voxel data textures also adds a keyframe for brightness, but animation doesn't work.

To reproduce:
Open blender
add voxel data texture to the cube
Insert a keyframe for the Intensity setting (under voxel data tab).
Open color tab: brightness setting is also green (these seem to be the same setting internally).
Go to another frame and add a keframe for intensity again.
Now scrub. Intensity does not animate.

Now go and do the same thing (start with new file) but this time, instead of animating intensity, animate the brightness setting. Intensity also turns green.
This time, the brightness setting animates properly, but the intensity setting doesn't animate with it, even though it's marked green, and thus should be keyed.