Waterlogged leaves don't spread water

I can confirm.

I recon this gets WAId to be equal to the mangrove roots.

Are we certain that this works as intended? I remember when mangrove roots were added water didn’t spread and I was under the impression that that was a bug, but people liked it so they kept it. However, I do not recall this being said about leaves. 

Was WAId by Mojang, check the history.