Ask yourself this question ; when walking, does your knee flex and retain that position momentarily, straightning only , as weight is fully applied ?.
Now step to a straight leg.. Q.. which is more " natural " ?.
These are 2 competing theories ...The Intern. style chose the straight one, nut, altho trained initially in that style, I've come over to the other.
Reason ?.. I prefer my "latin " to retain its indigenous style in looks and technique, with a blend of both.
The word "correct " depends upon whom one asks .