I am actually not sure entirely this is a bug or intentional (I just want an understanding).

Pretty much, before the 1.8 snapshots, if you made an invisible block, it would be invisible. Now, they are rendered black. If the item is held in the hand, the invisible textures are invisible. Only, once placed, will the item turn black. This is also true for slight transparency and half-coloured/half-invisible textures. This unaffects torches and possibly others.

If this was a feature/fix I missed, then feel free to tell me.