(hope this isn't a dup, quick check i didn't see one) This is a minor annoyance in the pager, aka "workspace switcher" - shaded/rolled-up windows (that is, showing only the title bar) are shown in the pager as full. Maybe they should be drawn simply as a line for the title bar, or simply ignored from the pager?
This is a bug / feature request for the libwnck pager widget, not our panel (which merely uses the widget).