This is not a bug:  Python, like many other computer languages, stores floats in binary.  The values 1.6 and 0.6 aren't exactly representable in the internal format used, so the stored versions of 1.6 and 0.6 are actually just very close approximations to those values.  It just so happens that the approximation for 1.6 is a tiny amount larger than 1.6 (the exact value stored is 1.600000000000000088817841970012523233890533447265625), while the approximation for 0.6 is a tiny amount smaller than 0.6 (the exact value is 0.59999999999999997779553950749686919152736663818359375).

I recommend looking at the appendix to the Python tutorial for more information about floating point:

http://docs.python.org/tutorial/floatingpoint.html