PyScripter is a Windows only IDE.  I am using the official release 
*** Python 2.7 (r27:82525, Jul  4 2010, 09:01:59) [MSC v.1500 32 bit (Intel)] on win32. ***

Python 3.2a2 fixes this since, according to SVN, str is now using the same code (or at least the same parameters to the _Py_dg_dtoa call) as repr.

I am afraid I do not have a minimal code to reproduce this, since the error only occurs with the python.dll embedded to PyScripter.  To reproduce with PyScripter you need to

a) Download and install the latest version of PyScripter from pyscripter.googlecode.com
b) Set the python engine to the internal (embedded python) using the menu (Run, Python Engine, Internal)
c) Execute in the interpreter window str(38210.0) etc.

The puzzling thing is that the same Python.dll when used by python.exe and not PyScripter produces correct results.  PyScripter does not mess up with built-ins in any way or set any special flags and I see no reason why results would differ.