I noticed this whilst adding a feature to the Flying Colors module…
Define a Mouse-Over layer with text below each piece.
The Ship pieces in Flying Colors have a layer that displays below the piece. At start, this layer is blank. When rigging hits are applied the layer changes to display rigging hits (it is a graphic rather than text).
The mouseover below-text obscures this layer. As a workaround, I found by increases the gap between pieces, the layer got room to display. See images. Bug 14523 raised.
[attachment=0]mouseover-layer in gap.png[/attachment]