_Some_ Grass Blocks Missing Bottom Texture

[AbbyRead]

I usually only see these on the underside of these clay pond overhangs, but the one where I ended up putting a campfire (If I remember correctly) I dug under and... generated? Forcing the block to transform into a regular ol' dirt block seems to alleviate it. I'm not sure if this is a bug with CE or Terrain, but I've only seen it when using Terrain. That might just be because of some different circumstances that are provided by BTA world gen though. Opportunity to see it maybe. Anyhoo.

Single Player
BTW-CE-1.3.6-client
BetterTerrainAddon-2.0.6-client
Quieter MillStone-client

Steps to reproduce: Upskirt grass blocks until you find one that's... a little different.