Sidebar not rendering properly in mobile Chrome

The sidebar doesn’t appear to be rendering properly in mobile Chrome (both iOS and Android) in the narrow/portrait orientation. The corner “plus” popout button works and shows the sidebar menu, but when the page is scrolled down at all, the contents in the sidebar shift down leaving empty space at the top. The sidebar contents seem to shift down to align vertically with the main page contents (just below the mobile menu bar “button”).

Have also tested it in mobile Firefox (Android) and mobile Safari and it seems to work fine in those browsers. Have not had an opportunity to test under Windows 8 mobile.