Have the debugger open, stopped on a breakpoint, and save the open file. The whole thing will bomb after the save finishes. Changes are not lost, but I have to reopen IDLE and lose history and breakpoints.

What operating system are you using?  Which python 3.2 are you using (i.e. a particular installer downloaded from python.org, built from source, etc)?  If known, which version of Tcl/Tk are you using?

With 3.2.3 (on OS X), if I open a new edit window, enter a few files, save the file, set a breakpoint on a line, then save the file again (with or without having debug on), the following exception occurs but IDLE keeps running:

Exception in Tkinter callback
Traceback (most recent call last):
  File "/Library/Frameworks/Python.framework/Versions/3.2/lib/python3.2/tkinter/__init__.py", line 1399, in __call__
    return self.func(*args)
  File "/Library/Frameworks/Python.framework/Versions/3.2/lib/python3.2/idlelib/MultiCall.py", line 166, in handler
    r = l[i](event)
  File "/Library/Frameworks/Python.framework/Versions/3.2/lib/python3.2/idlelib/IOBinding.py", line 336, in save
    self.editwin.store_file_breaks()
  File "/Library/Frameworks/Python.framework/Versions/3.2/lib/python3.2/idlelib/PyShell.py", line 214, in store_file_breaks
    self.update_breakpoints()
  File "/Library/Frameworks/Python.framework/Versions/3.2/lib/python3.2/idlelib/PyShell.py", line 244, in update_breakpoints
    linenumber_list = self.ranges_to_linenumbers(ranges)
  File "/Library/Frameworks/Python.framework/Versions/3.2/lib/python3.2/idlelib/PyShell.py", line 250, in ranges_to_linenumbers
    lineno = int(float(ranges[index]))
TypeError: float() argument must be a string or a number

In a quick attempt, I was not able to produce the same exception with 3.3.0rc3.

This was fixed in issue9803, but after the 3.2.3 release. I'm closing this issue as a duplicate.