I can't reproduce this with py3k on linux, but I do get a traceback in
the terminal used to launch idle:

Exception in Tkinter callback
Traceback (most recent call last):
  File "/home/ajaksu/py3k/Lib/tkinter/__init__.py", line 1399, in __call__
    return self.func(*args)
  File "/home/ajaksu/py3k/Lib/idlelib/MultiCall.py", line 165, in handler
    r = l[i](event)
  File "/home/ajaksu/py3k/Lib/idlelib/EditorWindow.py", line 315, in
home_callback
    if self.text.compare(first,">",last):
  File "/home/ajaksu/py3k/Lib/tkinter/__init__.py", line 2844, in compare
    self._w, 'compare', index1, op, index2))
_tkinter.TclError: expected boolean value but got ""

That only happens sometimes happens, pressing home while holding shift
down does nothing but print the traceback. Else, pressing 'home' holding
shift alternates: start of line, start of indented block.