The problem seems to affect Python 2 too. See also #1268.
In the online doc 'w' is not mentioned but a note about the size of 'u'
that changes depending on the build should be added too.
Also in the table in the Python 2 doc [1] the "Python Type" for
'unsigned int' and 'signed long' seem swapped [2].

[1]: http://docs.python.org/library/array.html
[2]: Modules/arraymodule.c under "/* Description of types */"