Comment 3 for bug 769278

System monitor is wider because it has a minimum width of 821 px set. So if the screen width is less than 1642 px, the orange overlay and the window size don't match as compiz honors the requested minimum width.

The design team has decided that the correct way to handle this situation is to not display the overlay nor resize the window at all. Progress of that can be tracked in bug 723855.

So, the window being too wide is not a bug - the overlay appearing in that case is. Thus I'm marking this as a duplicate of bug 723855.

Thank you for reporting!