What I was attempting to say was that there's a reported bug about physical objects with volume detect on not detecting non-physical object collisions.
I tried it briefly in the preview before it was taken down and it still doesn't seem to work, but there were also a bunch of other issues and I didn't have enough time to really test it. It definitely doesn't work in the current version.
This is an exact example of why a real bug list would be useful. AFAIK, this bug has never been acknowledged, so is the current behavior what's intended, or was the bug deferred or lost?