Board Thread:Theories and Speculation/@comment-30355627-20170312130432/@comment-734582-20170312164905

Kakashisologod wrote: @Thekillman he had the option to:Absorb all of their jutsus,absorb their chakra and somehow BZ can walk up to him and he dosent sense he is trying to kill him. pretty much every power in Naruto is an active power, even "passive" ones like sensing, sage mode, etc. Madara wouldn't know Black Zetsu would backstab him unless he was trying to figure that out.

And well, as Black Zetsu mentioned, Madara couldn't conceive of the idea that he would be backstabbed by Zetsu. After all, BZ had successfully convinced Madara that he was his will. You don't expect your own will to backstab you. Since BZ is a creation of Kaguya, it's questionable that it has emotions, so Kurama's power wouldn't help Madara. Master sensors like Minato couldn't sense Black Zetsu (or else he'd have known BZ was stealing Kurama).

So, it's doubtful that Madara could truly sense Black Zetsu. He did have some sort of telepathic connection to BZ, so it's possible Madara hadn't even realized this