Original ticket http://projects.scipy.org/numpy/ticket/1085 on 2009-04-15 by trac user tillmann, assigned to @charris.

import numpy as np
x=np.array([[1,2],[3,4]])
print x
[[1 2]
[3 4]]
x+=x.T
print x
[[2 5]
[8 8]]

when writing code on such a high level of abstraction this behavior is not expected and imho wrong. At least a warning should be issued or better the in place operations should fall back to creating copies if the results are not correct otherwise.