JInternalFrame BackgroundShadowBorder line is longer in Mac Look and Feel.
Step to reproduce
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1) Run SwingSet2 in Mac Look And Feel
2) Select Internal Frames Demo.
3) Observe that JInternal Frame top BackgroundShadowBorder line. If you see the line passing the curve of the rectangle then the bug is reproduced.

I have attached the screen shot of the same. Just to make the line visible I modified AquaInternalFrameUI.java class to show the BackgroundShadowBorder line to be red. I have attached the screen shot of the same.