sin(0.25) that as far as I understand resolve to sin(0.25 PI 2) returns -1 counter intuitive to traditional math +1

Is this intentional?

additional question:

is there atan2 hiding somewhere?

Yeah, seems odd. sin(PI/2) should return 1

For atan2 see: https://www.lexaloffle.com/bbs/?tid=1887
Not part of the engine yet, but probably will be.