Panda3D and Tk - event scheduling problem under Mac OS X?

I have installed the Panda3D-1.6.0-pre.dmg package under MacOS X (Leopard). My application consists of two windows - the Panda3D and a TkinterGUI. When starting the application both windows appear, but it’s hardly possible to interact with the Tk GUI. It seems that not all events on the Tk window are processed.

Example code:

import direct.directbase.DirectStart
import Pmw
import Tkinter 

def sayhello():
    print "hello"

root = Pmw.initialise()
b = Tkinter.Button(root,text="hit me",command=sayhello)
b.pack()

base.startTk()
run()

When executing this code two windows appear - the Panda3D and a TkInter GUI with one button “hit me”. Events on the Panda3D window are processed immediately, but not the activites on the Tk window. Try to switch between the windows and you will recognize the problem.

The problem occurs only under MacOS, not under Windows.

Versions:
Mac OS X: 10.5.5 (Leopard)
Panda3D: 1.6.0pre
Python: 2.5.1

Has anybody a solution for this problem?