This bug has been opened here: https://bugzilla.ubuntu.com/show_bug.cgi?id=16846

"When I use alt-tab to switch between windows, I see the outline of the window
drawn before I let go of the alt key.

This works for all windows other than maximised ones.

The code in metacity's screen.c calculates values for 'east' and 'south' both as
zero when the window is maximised, and ends up drawing the outline outside the
visible screen area.

For example, my screen is 1024x768 pixels.

A maximised window's frame is 1024x719 pixels, and the windows (non-frame)
content is 1024x696 pixels.  Note that the frame is just a 23 pixel tall title
bar across the top - maximised windows don't have the 5 pixel wide border around
them that other windows have.

The two rectangles which end up being used to draw the frame are of sizes
1023x718 and 1025x720 respectively, which don't show up on my display.

I've attached a patch which uses the #defined value of OUTLINE_WIDTH whenever a
frame of width 0 would otherwise be drawn.

https://bugzilla.ubuntu.com/attachment.cgi?id=4273
proposed patch"