If you resize the screen to a smaller size via xrandr any windows that would no longer be visible should be re-placed inside the new viewable area. This works fine for settings manager, but iconbox, panel, taskbar (and perhaps others) are not moved onto the viewable area and are lost.
Additional information: Example: panel sits at bottom of 1600x1200 screen. xrandr resize to 1280x1024 and the panel is still sitting at the old 1600x1200 location (bottom edge is still at 1200) instead of being moved to new location where bottom edge is at 1024.
xfwm4 replace windows with borders, assuming the others would repalce themselves. Unfortunately, for now only xfwm4 is xrandr compatible, so the others are left out (support for xrandr was added in xfwm4 for apps like xawtv which use xrandrd to resize the output fullscreen window) This should be improved in xfce 4.2. Olivier.
What do we do with this bug? I believe the panel is xrandr aware at least when compiled with gtk > 2.2. Any other Xfce problems?
I added the xrandr support to panel, taskbar and desktop one week after 4.0 was released. It works only with gtk+ 2.2, but no problem here, since this is the target plattform for 4.2 anyways.
Should be fixed for builds using gtk >= 2.2.