Field.real/imag copy arrays, contrary to documentation

import nifty as ift

a=ift.RGSpace(10)
f=ift.Field(a,val=1.+1j)
f.real.val+=2
f.imag.val+=2
print f.val

This prints '1+1j' as the field value, i.e. the manipulations of real and imaginary parts did not affect the original field. This seems to contradict the documentation, which states that the data is not copied.