It's possible it's intentional (though this would have been 7 years ago now, and I doubt I can find original conversations about it), but it's more likely it is an obscure oversight that no one noticed until you did.
I'll inquire about fixing it, unless it is actually intentional.
I just discovered that both Dynasty Shingles AND Coralstone Blocks also do not block light. The significance? All 4 were added roughly sequentially, at the same time. I suspect someone simply forgot to add the "blocks light" flag while adding all of these at the same time back in 2014, and it was never noticed.
However, I'm now very curious to investigate if there are any others.