1/(4/3)(1/8) is 6, but the result of (4/3)(1/8) used as the denominator with 1 as the numerator give you 5.999...
Is this due to the limitations in the amounts of decimals the calculator can hold?
I get 6 in both cases. It is rounding off error in your calculator.
I also got '6' as the answer using the calcualtor on this site....