This bug is best demonstrated in the video attached.

There appears to be an inconsistency to which blocks receive power when positioned under a top half slab (or other transparent block on which redstone is able to be placed), with active redstone ontop of it.

The expected behavior would be that no block positioned under the transparent block would be powered, however Droppers, Dispensers and Pistons do activate, while all other blocks, such as redstone lamps, trapdoors etc. don't.