GTK: SwingSet2 Taskbar not showing all internal frame icons in mercury

Platform: Mercury with Blueprint
L&F: GTK
Steps to reproduce:
- Run SwingSet2 with option -Dswing.gtkthemefile=<gtkrc file>
- Change L&F to GTK
- Dont change the default size of SwingSet2 frame i.e dont maximize it.
- Now using JInternalFrame generator, Open around 120-125 internal frames.
- Now on taskbar there should be icon for each internal frame.
- Click on the last internal frame icon visible on Taskbar,
  This should open or select the last internal frame, but inturn it will
  highlight some other internal frame. Now try searching the last
  frame(Say Frame 120) icon on taskbar, But it will not be found.
- Possible reason of this problem is that Internal frame icon have a minimum
  size, But since number of icons are more so that they cant be accomodated
  even with minimum size, So it start storing those icons in another row
  below it which is not visible.