Moss patches, when placed on the side of a block, can be placed while air is under them. This only works when it's a single block of air, though, more than that.

Moss Patches do not draw a texture on the bottom surface. Normally this wouldn't be a problem with just TF and vanilla as they should only be placeable on solid surfaces and decay if there is nothing under them, but other mods might have blocks that act as solid and thus expose a see-through side of the Moss Patch which ends up looking sloppy for us.

I'm renaming the ticket to "Moss Patch Fixes" so as to reflect this also being somewhat of an issue.