Graph with exponent not correct

[MullenJohn]

When I graph the function (X^2 - 4)^(2/3) on the HP Prime there is nothing showing between -2 and +2. (This also happens on my HP 50g calculator)

However when I rearrange the function to the form 3√(x^2-4)^2/3 the graph display properly between -2 and +2.

It appears the calculator cannot graph a fractional exponent to an expression within a set of parentheses.

Does anyone know why and if so is there a setting that need to be done?

Thanks - Cheers!