Relative speeds equal own speed when in different reference frames

When two craft travel at high velocitys, the speed relative to each other is displaying their own velocity(orbit and surface velocitys practicaly equal). This only happened while the two craft were in different reference frames.
Potentially relevant: when launching the faster craft, the displayed velocity took a few seconds of 19x slow motion to reach the correct value, accelerating as if on a fast rocket instead of instantaneous, like it should have.
Since the velocitys of the crafts are so great and the difference between the velocitys is on the same magnitude the bug becomes apparent.