Issue description:

Refined Storage seems to try to cast realworld.block.BlockRWSlabDouble into net.minecraft.block.BlockSlab for using them as covers, which causes the game to crash.

Version (make sure you are on the latest version before reporting):

• Minecraft: 1.12.2
• Forge: 14.23.4.2739
• Refined Storage: 1.6

Does this issue occur on a server?
Yes

If a (crash)log is relevant for this issue, link it here:

https://pastebin.com/CT67fq5r

RealWorld issue. RS doesn't cast, but RealWorld casts, something which the stacktrace shows.