Broken: Blender on Windows built with MSVC 11.0 or later (includes 2.71 release)
Worked: 2.70a and earlier
When Blender is called from a subprocess with no STDOUT available, the Py_Initialize procedure will cause a fatal error, due to a bug in more recent MSVC versions. (This issue will be fixed in MSVC 14)
The respective Issue on the Python Tracker:
This breaks the Auto-Import functionality for blend files in Unity (unity3d.com), where a .blend dropped in an asset directory will be automatically converted to FBX by calling the Blender executable (and the FBX exporter python module).
I can confirm that a possible workaround outlined at http://bugs.python.org/issue17797#msg201964 fixes the issue. This would imply modifying pythonrun.c and replacing the Python34.dll with a modified version.