Error in Biome Generation in Dimensions

When I create a custom biome to implement as a base biome for my dimension (overworld generation) I am finding that only the grass block (ground block) is generating, and is also overwriting where the dirt block (underground block) should be generating (underneath the grass block is more grass blocks rather than dirt). I am certain this is a bug because regardless of what I change the underground block to, the biome is only ground blocks. All secondary and tertiary blocks in the dimension are also the dirt block and not the grass block.