prior to bug fix, if you opened the nav menu then closed it without a
page reload, you would find a horizontal scroll on the main page with
overspill to the right hand side.

…hen a submenu is opened extending below the screen.

Common issue can be recreated easily.

Take an iOS touch device, make the navigation so that when the  nav
draw is opened then the submenu is opened it extends past the bottom of
the screen requiring a scroll to see the links, the drawer content
wouldn’t scroll, prior to the css fix.