This might be a browser issue, I don't know, but it seems to have only started recently.
If I place the cursor on the horizontal bar, it stays as the typing cursor and doesn't change to the arrow cursor, thus making it impossible to click and scroll left and right--only on very rare occasions will it work. Even the vertical bar sometimes acts up. Although I should note that it works fine on the overlays, such as when clicking View Custom Changes. It's only an issue in the actual templates for some reason.