Debug mode shows invalid block IDs

I know how to code,so i know this,i see in debug mode blocks that has a name (Example:double_stone_slab)which is invalid and unknown by the game in itself.There are also invalid data,which is actually still known by the game,but although this data doesn't exist.For another example:double_stone_slab 8.It works in MCPC 1.7.10,but not in 1.8.1-14w01a.I don't know why,this is strange.I have double-checked the IDs exists,they don't.They are not even wrote in the code.I shouldnt give you my code logicial to see the minecraft's code,you may do errors while trying to fix my problems.