The new version runs 40 parabolas, then quits. I usually have to run this version 20 times or so to get the crash, so be patient. In general if it's going to crash it does so in the first 6 or so parabolas. Caveat: creates up to 40 threads, so a bit of a CPU pig. You may want to change the 40 in (self.tracks > 40) to 8.

Here's one crash. I got this by double clicking the .py file from Windows explorer, but I can get them with F5 in IDLE too.
---
UpdateStringProc should not be invoked for type cmdName

This application has requested the Runtime to terminate it in an unusual way.
Please contact the application's support team for more information.
Exception in thread Thread-6:
Traceback (most recent call last):
  File "C:\Python27\lib\threading.py", line 530, in __bootstrap_inner
    self.run()
  File "H:\PMT2\MyProjects\TkinterCrash2.py", line 47, in run
    self.deliverToQueue((self.target, z, y))
  File "H:\PMT2\MyProjects\TkinterCrash2.py", line 129, in arrival_122
    new_yz[1])
  File "C:\Python27\lib\lib-tk\Tkinter.py", line 2201, in create_line
    return self._create('line', args, kw)
  File "C:\Python27\lib\lib-tk\Tkinter.py", line 2189, in _create
    *(args + self._options(cnf, kw))))
TclError: bad screen distance "create"