'cause I love twitters Bootstrap and want to give it a try in my own blog I did a local test-install yesterday and stumbled across this bug, too. So I came in here and found the solution, great!
What I also did was to cut out the BS4.0.0 code from style.css and theme.js and added the actual 4.5.0 files manually before these two files in index.tpl and preview_iframe.tpl. Now I have to find out how to do this in a more elegant way.