I did a quick test of this, and it looks like this only occurs when your shadow setting is on “Low.” Note that the “High Quality Shaders” option does not affect this.
The two images above show that Low shadows cause the projector light to pass through objects.
The two images above show that Medium shadows cause the projector light to be blocked by objects.
Perhaps this is intentional, as there are probably less checks with allowing the light to just pass through objects and therefore that would reduce lag. If not, then this is certainly something to look into.