SwingUtilities.updateComponentTreeUI(frame) doesn't validate and repaint the frame completely, only some components get refreshed.
Switching between JLF and motif look-n-feel in my test app resulted in some components have motif look and some have JLF look if only these two line of code are used:
       UIManager.setLookAndFeel(uiFactory);
       SwingUtilities.updateComponentTreeUI(frame);
I have to add the following code to make the app (frame) refresh completely.
         frame.invalidate();
         frame.validate();
         frame.repaint();
 
I would think that a validate/repaint should be automatically done for the WHOLE FRAME after a updateComponentTree(frame) call.