It's not perfect, no. After messing around and updates, I actually came to point in your situation. What I had to do to remedy it was a refresh. Re-installing 8.1 has fixed my issues for now. I've also tried updating the driver from Intel also, but that didn't work well either. I ended up with a boxed resolution an inch smaller than my TV display. So, I wouldn't mess with that one.
I'm afraid to update the newest Defender from 7/31 in fear of it being broken again. I don't know what is causing the issue, but this is the only solution i've found so far. Hopefully someone more knowing will have an answer for us or it gets resolved in 8.1 final soon.