Original ticket http://projects.scipy.org/numpy/ticket/1200 on 2009-08-19 by trac user dgoldsmith, assigned to unknown.

c = np.array([' aA '], dtype='S6').view(np.chararray); c
chararray([' aA'],
dtype='|S6')
len(c[0]) # is 'A' the trailing character...
4
c.rstrip('A') # ...or not?
chararray([' aA'],
dtype='|S6')

Note:

len(c.base[0]); c.base[0]
6
' aA '

Consequent hypothesis: rstrip is operating on c.base, not c.

len(c.base[0]); c.base[0]
6
' aA '