Running on Debian Lenny, with Python 3.1.
The Python 2.5 version is OK.

~ $ python3 --version
Python 3.1.1+
~ $ python3 -m doctest
F..............
======================================================================
FAIL: Doctest: __main__.DebugRunner
----------------------------------------------------------------------
Traceback (most recent call last):
  File "/usr/lib/python3.1/doctest.py", line 2096, in runTest
    raise self.failureException(self.format_failure(new.getvalue()))
AssertionError: Failed doctest test for __main__.DebugRunner
  File "/usr/lib/python3.1/doctest.py", line 1644, in DebugRunner

----------------------------------------------------------------------
File "/usr/lib/python3.1/doctest.py", line 1712, in __main__.DebugRunner
Failed example:
    runner.run(test)
Expected:
    Traceback (most recent call last):
    ...
    doctest.UnexpectedException: <DocTest foo from foo.py:0 (2 examples)>
Got:
    Traceback (most recent call last):
      File "/usr/lib/python3.1/doctest.py", line 1243, in __run
        compileflags, 1), test.globs)
      File "<doctest __main__.DebugRunner[15]>", line 1, in <module>
        runner.run(test)
      File "/usr/lib/python3.1/doctest.py", line 1736, in run
        r = DocTestRunner.run(self, test, compileflags, out, False)
      File "/usr/lib/python3.1/doctest.py", line 1375, in run
        return self.__run(test, compileflags, out)
      File "/usr/lib/python3.1/doctest.py", line 1296, in __run
        exception)
      File "/usr/lib/python3.1/doctest.py", line 1742, in
report_unexpected_exception
        raise UnexpectedException(test, example, exc_info)
    UnexpectedException: <DocTest foo from foo.py:0 (2 examples)>


----------------------------------------------------------------------
Ran 15 tests in 0.015s

FAILED (failures=1)
~ $

Apparently this was introduced with r51625 :

r51625 | guido.van.rossum | 2006-08-26 16:37:44 -0400 (Sat, 26 Aug 2006) 
| 4 lines

Inspired by SF patch #860326, make the exception formatting by
traceback.py be closer to the built-in formatting.
A few unittests had to be fixed, too.

------------------------------------------------------------------------


When doctest is imported as __main__, traceback does not prepend 
UnexpectedException with doctest. prefix.  Attached patch fixes the 
issue by explicitly reimporting doctest in the 'if __name__ == 
"__main__":' clause.

This is rather inelegant and a better solution would probably be to use 
python -m doctest for something other than self test.  For example, 
running doctest.testfile on command line arguments would be a reasonable  
use, but python -m doctest Lib/doctest.py may still have a problem.

python -m doctest does accept file arguments.  Running the self-test is
the default if no arguments are supplied.

python -m doctest Lib/doctest.py passes.

So perhaps we should just remove the default and instead issue an error
message about missing arguments.

I am ok with the proposal of removing the current "selftest" default
behavior.

And thank you for the tip.
I tried the command "python -m doctest Lib/*.py" and I found interesting
things:
 * #7379 about Lib/fractions.py
 * #7380 about Lib/uuid.py
 * #7381 about Lib/subprocess.py

;)

Patch proposed.

Patch could be applied to Python 2.6 and trunk too.

Minor update: replaced '{}' by '{0}' for compatibility with 2.6.

Ready for review and merge.

The patch results in this type of usage message:

usage: /home/rdmurray/python/trunk/Lib/doctest.py [-v] file ...

which while technically correct isn't the way I called it.  It would be
better to at least use basename on argv[0].  (I wonder if there's some
way for a module to know it was called via -m...).

Variant which gives different usage messages:

~ $ ./python -m doctest
usage: doctest [-v] file ...

~ $ ./python Lib/doctest.py
usage: Lib/doctest.py [-v] file ...

I has already adjusted the patch, in a slightly different fashion, but
to much the same effect.  Checked in to trunk in r76935.

The bug doesn't exist on 2.6, so I'm not backporting.  Ported to py3k in
r76937 and backported to 3.1 in r76938.