As of 1.2.13, all cliffs, overhangs, and floating islands landscape having only stone being visible below them. It is making the landscape look pretty ugly and does not mesh well with the surrounding Grass and terrain. I tested this bug on my Windows 10 computer running MC on v.1.2.13 and on my iPhone running MC on v.1.2.15
What I believe is happening is all decorative surface block that has a non-transparent block above it (which is blocking sunlight) will not let the decorative surface block spawn.
I included several pictures showing this new change but trust me, it looks a lot worse in person than in pictures. It affects all biomes except for the Mesa biome it seems.
Some seeds you can try to see this for yourself are: 1423683032 has the Ice Spike overhang at 280, 80, 270 | GODmedpups has a Birch Forest M overhang at -10, 88, 250 (Birch Trees are still bugged to being short in Birch Forest M but that a different bug report) | and lastly, 1421236222 has a Jungle overhang at 570, 70, 50.
The new change looks really bad that I am pretty sure this has to be an unintentional terrain generation and a bug/side-effect. If this is confirmed by Mojang to be an intended change, then I question their sanity and will voice my opinion on their feedback page So for now, I believe it is best to view this as a bug that needs to be patched.
Edit: Changed my tone to be less negative. Also, Tommo at Mojang saw my Reddit post about this change and he says it may be a bug: https://www.reddit.com/r/Minecraft/comments/8c83up/in_bedrock_edition_mojang_removed_grass_from/dxe5ebx