Disabling interpolation for Z rotation within animation window?

I have a 2D sprite animation consisting of three frames. The sprite is of a spotlight panning from left to right over 3 discrete frames. I have added a beam of light (sprite) that rotates alonsgide the z axis and am also automating it's position to follow the animation of the spotlight sprite. The problem is that the added beam sprite's motion is is interpolating all over the place when running the game, but not when scrubbing through the keyframes.

Note: I have set both tangents to constant, and the curves window display flat steps between keyframes, yet it still interpolates. I've been tryng to figure this out forever and am pulling my hair out, please help!