Fence holds on to nothing

So I was trying to build lantern things, and I was placing a block near crowded sheep and I made a glitch fence, it took the block number but when I placed another in that spot it wouldn't use the block, instead, it thinks the block I placed is the original block, its weird, its invisible and you cannot collide it, but the fence you can collide it for some reason, but for some reason, the sheeps can't walk thru the invisible block but you can, when you place a flower on that block it destroys it, so you can get the block you place after you have placed something on that block, and the fence resets back, would love to send the video but 10mb limit, f3 and a does nothing but relogging, will revert ur fence and give you your block back.