Voxel Grid with XYZRGBA cloud

Brought the discussion from the mailing list, because I think this a bug.

I just gave it a try at voxel grid filtering using a XYZRGBA cloud, where all my points had alpha set to 1, and I was quite surprised to discover that all the points in the filtered cloud points had alpha set to 0.

Is there any particular reason which makes it impossible for voxel grid filtering to handle alpha values? 
