[CurveEditor] Dragging keyframes after shift selection gives erroneous results

Repro:
1- Open attached project.
2- Open scene 'asdf'.
3- Select 'Cube' game object.
4- In curve editor, select one keyframe on either position x, y or z curves.
5- Range select other keyframes on x y and z curves.
6- Drag box around.

You'll see that keyframe that was selected first does not move with the rest of the selection.