My phone is on 8.1 Update still and what you wrote is not true for my phone, but what the OP said is. For example, I go into Messaging, I tap the very left edge of the bar, it expands. I tap again in the blank space a little to the right (still on left side of the '+' icon which is on the left side of centre) and nothing happens. I tap just to the right of the Search icon (first icon right of centre), nothing happens. I tap the 3 dots, it expands. The whole bar is *not* active as you stated. I tested in 4 different apps, same.
I do not know at what point the behaviour changed.