I also can verify that the problem is not reproducible using a current 
trunk (2.7) and the 10.6 Apple Tk 8.5.7.  Further testing of this issue 
with both Apple Tk 8.4.x and ActiveState Tk 8.4.19 on 10.4, 10.5, and 
10.6 has been hang-free.

It looks like there were a number of fixes to _tkinter.c and friends 
checked in by Guilherme early in 2009 that were not backported to 2.6 
and some of them have to do with thread locking.  Whether or not the 
fixes should have been backported is not an issue at this point. However 
I think it makes little sense to attempt much further work on this 
problem using the current 2.6 base without looking at backporting first.

So, with regard to the 2.6.3 release, I concur with Ronald's plan to 
continue to link only with Tk 8.4 for the OS X installer and I suggest 
there be a disclaimer somewhere about building with Tk 8.5 on OS X for 
2.6.3.