I'm using the <!--more--> quicktag to limit how much of each post shows on the home page. When I activate Preserved HTML Editor Markup the location of the quicktag no longer shows in the visual editor. The quicktag is still visible when I switch to the text view editor.
I switched to the Twenty Twelve, Twenty Thirteen, and Twenty Fourteen themes and the problem remained so the problem isn't with my theme. When I deactivate Preserved HTML Editor Markup the quicktag location reappears in the visual editor.