In the SwingSet(JDK1.1.5 + Swing-Pre-1.0(1/29) + WindowsNT4.0):

1) click Internal Frame tab.
2) check isMaxable, isIconifiable, isResizable boxes.
3) create 2 internal frames.
4) Iconify only one frame.
5) Change to motif look.
6) Change back to windows look.

Iconified frame doesn't have iconify button and size was not resized. And its bound area was same with motif icon(square rectangle) with blue background.

7) maximize and minimize it
8) when you maximize again, it disppeared.