Just for clarity, F10 opens the Code Inspector Window, not Code View, which is a Document Toolbar option that affects the Document Window.
1. I have both the CSS Designer and the F10 Code Inspector open as floating windows (not locked to the app frame)
2. Created a new responsive page using the New > Starter Template > Responsive Starters > About
3. Saved the page to my Defined Site
4. With only Design View open (not split view) close the page
No crashes on either machine.
I tried again with different combinations of windows locked to the app frame (but not as pop-outs) and design vs design/code split view, I also alternated between Ctrl + W and clicking the X in the Document Window to close it, still no crashes.
Then I dragged the CSS Designer to fill more of my screen, until it turned into that obnoxious, totally unusable 2 column monitor filling horror. It didn't crash on close, but exploded when I tried to reopen the file. I restarted the program and it crashed on closing the file 2 out of 3 times.
Narrowed the CSS Designer back down to a normal 1 column window, no crashes.
Looks like a bug to me: Feature Request/Bug Report Form