On-screen buttons using buid.props results in an empty bar

So I have a Samsung tablet (SM-T800) and I have it rooted running the stock rom. I really want to enable on-screen buttons and disable the hardware buttons (I keep hitting them by accident all the time when I read comic books. I hate them).

So all the instructions I've see have invovled editing the

Code:

---

build.prop

---

and adding

Code:

---

qemu.hw.mainkeys=0

---

. When I do that and reboot, I get a black bar at the bottom of the screens in most of my apps with no buttons on it. I assume this is the on-screen nav bar, but for some reason, all the buttons (Home, back, app select) are missing. I know on my phone where I run Cyanogen, you can customize which buttons show up. I was wondering if this was configurable somewhere and if, in Samsung's stock rom, they disable all of them? Or is it something else entirely?

What am I missing?