Smooth sandstone's bottom texture is that of ordinary sandstone

The bottom face of smooth sandstone, which previously (in at least some 0.14 versions - don't recall exactly which) was smooth like the top, has the cracked pattern of the bottom of 'standard' sandstone. Ceilings made of smooth sandstone subsequently have drastically altered patterns from the intended design.

Attached screenshot shows regular sandstone on the left, smooth sandstone on the right.