Behaviour on x {} does not work consistently

In the attached example the x value is not updated each time the mouse is released. The first time if released on the left side of the threshold it works, the second time, also on the left side of the threshold it does not work. The target blue box does not return to the edge. If alternating releasing on the left and right of the threshold it works.

The target blue box does return to the edge if the Behaviour on x {} is commented out.