unconsistent slicing + setting of values
I'm not sure if this is intended behaviour that I don't yet understand, or a bug.

I have a DataFrame df
              A         B         C
    0 -1.191583  1.290778 -0.445384
    1 -1.275654 -0.716870  1.068261
    2 -0.179524 -1.783951  2.539275
    3 -0.149163  0.621901 -0.326219
    4  0.055287 -0.057617  1.015610
    5 -0.816133 -0.505380 -0.480527
    6  0.531102  0.292489  0.362619
    7 -0.467907  0.179168 -0.892605

I want to set some values by generating the correct slice, and then passing an array:
    df[:4]['B'] = range(4)
but df remains unchanged.  However, if I change the order of the slicing, it works:
    df['B'][:4] = range(4)
    df
              A         B         C
    0 -1.191583  0.000000 -0.445384
    1 -1.275654  1.000000  1.068261
    2 -0.179524  2.000000  2.539275
    3 -0.149163  3.000000 -0.326219
    4  0.055287 -0.057617  1.015610
    5 -0.816133 -0.505380 -0.480527
    6  0.531102  0.292489  0.362619 
    7 -0.467907  0.179168 -0.892605

Is this normal? 
Thanks,
Roel
