I get a nearly identical failure building Python 2.6.2 on a SPARC64
machine running Solaris 5.10 using GCC 4.1.1.

# ./python ./Lib/test/test_ctypes.py
...
test_longdouble (ctypes.test.test_callbacks.Callbacks) ... FAIL
...

======================================================================
FAIL: test_longdouble (ctypes.test.test_callbacks.Callbacks)
----------------------------------------------------------------------
Traceback (most recent call last):
  File
"/home/build/clifford/gpdb/tools/python/2.6.2/objs/sol10_sparc_64/Lib/ctypes/test/test_callbacks.py",
line 81, in test_longdouble
    self.check_type(c_longdouble, 3.14)
  File
"/home/build/clifford/gpdb/tools/python/2.6.2/objs/sol10_sparc_64/Lib/ctypes/test/test_callbacks.py",
line 30, in check_type
    self.failUnlessEqual(self.got_args, (-3, arg))
AssertionError: (-3, 0.0) != (-3, 3.1400000000000001)

----------------------------------------------------------------------
Ran 319 tests in 1.951s

FAILED (failures=1)
Traceback (most recent call last):
  File "./Lib/test/test_ctypes.py", line 12, in <module>
    test_main()
  File "./Lib/test/test_ctypes.py", line 9, in test_main
    run_unittest(unittest.TestSuite(suites))
  File
"/home/build/clifford/gpdb/tools/python/2.6.2/objs/sol10_sparc_64/Lib/test/test_support.py",
line 722, in run_unittest
    _run_suite(suite)
  File
"/home/build/clifford/gpdb/tools/python/2.6.2/objs/sol10_sparc_64/Lib/test/test_support.py",
line 705, in _run_suite
    raise TestFailed(err)
test.test_support.TestFailed: Traceback (most recent call last):
  File
"/home/build/clifford/gpdb/tools/python/2.6.2/objs/sol10_sparc_64/Lib/ctypes/test/test_callbacks.py",
line 81, in test_longdouble
    self.check_type(c_longdouble, 3.14)
  File
"/home/build/clifford/gpdb/tools/python/2.6.2/objs/sol10_sparc_64/Lib/ctypes/test/test_callbacks.py",
line 30, in check_type
    self.failUnlessEqual(self.got_args, (-3, arg))
AssertionError: (-3, 0.0) != (-3, 3.1400000000000001)