In the scripting Python console, type:

>>> Vector(1, 2, 3)
Traceback (most recent call last):
File "<blender_console>", line 1, in <module>
TypeError: mathutils.Vector(): more then a single arg given

The error message should read "more than", not "more then".

Found on Blender 2.66a on Win8

PS: I can write a patch, so feel free to assign to me. However, I'm currently in Singapore so even downloading Blender's source code takes a long time.