Incorrect results and quirks

[B1nary0]

First off, I am not a calculator, nor math buff,... but I have been getting some very strange and inconsistent results out of my HP prime, and I would like to see if anyone can help me figure out why (or at least how to work around the issues).

Issue#1: When I graph the function:
F1(X)=(X^2-4)^(2/3)

It does not graph -2 < X < 2,... it returns "NaN" for that region.

When I graph the same function using this form:
F1(X)=(3 NTHROOT (X^2-4))^2
(either using the NTHROOT command, or using the NTHROOT symbol to get the cube root in textbook entry mode)

it does graph the middle region,....

I'm not sure why it evaluates these two expressions differently, my TI-nSpire handles it correctly

Issue #2: Incorrect result returned when passing a matrix containing a negative number to an expression.
I will use the variable quirk to use in several forms of function (on the screen, and written as programs) and evaluate it for the value of "-1" and for 2 matrices, one with a -1 in the first position, the other with 1 in the first position.

The expression is: (screenshot attached since I can't type it easily here)
2-2/(3 NROOT quirk)

quirk:=-1
returns: 4 (correct)

quirk:={-1, .5 , 2}
returns: 1+1.73205080757*i, -0.51984209979, 0.412598948032 (first value is incorrect)

quirk:={1, .5 , 2}
returns: 0, -0.51984209979, 0.412598948032 (correct)

To explore a little further, I wrote two programs, the first, testeval:
EXPORT testeval(quirk)
BEGIN
RETURN (2-2/(3 NTHROOT quirk));
END;

quirk:={-1, .5 , 2}
testeval(quirk)
returns: 4, -0.51984209979, 0.412598948032 (ALL CORRECT!!! WTF)
and returns the same values as the previous expression for the other two values of quirk

The second program I wrote, testeval2
EXPORT testeval2(quirk)
BEGIN
RETURN (2-2/quirk^(1/3));
END;

returns the same value for the matrix with all positive numbers, but returns an error when quirk=-1 or a matrix with a negative number in it
"Error:(X<0)^(∉Z)"

So,.... I'm totally confused and feel like I can't rely on my HP Prime,... sigh,... I hope someone here has a little insight.