When sing IDLE in Ubuntu (Jaunty) if you open the Class Browser and
double click on a class or function name, the corresponding section is
highlighted in the code in the Editor Window. 

If you again double click on another class or function name, the new
code section should be highlighted in the Editor Window but isn't.
Nothing happens. You have to first close the Class Browser window,
reopen it and double click on another name to select it the Editor Window.

In the Windows versions, successive double clicking will highlight the
desired selection in the Class Browser window.