....where "unexpected" means I didn't expect it. This may just be a documentation fix, or maybe I will be scolded for not realizing how np.ma works, but I don't think this behavior is appropriate:

In [100]: x = np.ma.ones(5)

In [101]: x.mask = [False,False,True,False,False]

In [102]: np.copy(x)
Out[102]: array([ 1.,  1.,  1.,  1.,  1.])

In [103]: np.ma.copy(x)
Out[103]:
masked_array(data = [1.0 1.0 -- 1.0 1.0],
             mask = [False False  True False False],
       fill_value = 1e+20)

In [104]: np.__version__
Out[104]: '1.8.0.dev-074a40c'

I would at least expect a warning, but would prefer to see, in order of preference:

• np.copy(x) returns a masked array (since x is a masked array)
• np.copy(x) warns that it is unmasking the array, then returns the same array as above
• np.copy(x) raises an exception
• np.copy(x) returns [1,1,nan,1,1] (this is probably not ideal)