Here is the scene from the outside. Very simple, 3 materials. The bottom of the lake is a plane, and the water is a volume with a specular material applied with a scattering volume node attached.

When I go inside the lake mesh to get a view under the lilypads, all the volumetric effects stop


I am using the pmc kernel as well.
If this is not a bug, I would like to report it as a suggestion so that you can be inside the volumes.