Closing the editor has always been a tad buggy. I don't run it in 10 so can't speak to that issue specifically.
For the main issue, I was sort of confused about how you phrased it.
but after this it doesn't bring up a blank level, but rather a tab that is titled "Eyes of a Child" that has loading screens and music playing.
So you can never get past the generic D:OS loading screen? A new blank level has no terrain btw, so it will look completely grey. Does it work if you try and load the main game in the editor?
The music continuing to play is an annoying bug, I can tell you how to sort of fix that one later once you get a level working.