@Matsv First issue: Thanks. Second: Ok, is it not to do with armour stand sizes? I can try comparing armour stands riding entities in 1.8 & 1.9, of one small one normal sized. Third: One I made, its a very obscure issue and probably not worth fixing. I ended up ditching the BlockCanBuildEvent and just did EntityPlayer.k = true to turn on invisibility, which fixes spec blocking. Thanks.