problem with DisplayPanelJ3D

Hello, I have some trouble when adding a DisplayPanelJ3D in a
JInternalFrame.
Actually, the DisplayPanelJ3D hiddes every other DesktopPane's
JInternalFrame, and
even every component of my main Frame!.

I have tried to modify the layer of the JInternalFrame containing the
DisplayPanelJ3D, but it doesn't work.

When using a DisplayPanelJ2D I don't have this kind of problem, why?

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