Adjusting motor speed of the hingejoint2D on "piece2" while in play mode. Object starts to move uncontrollably (flickering).

Note: Only happens in play mode while changing motor speed.

To reproduce:

1. Open scene.
2. Enter play mode.
3. Select "Piece2" game object.
4. Slowly adjust Motor Speed setting. (slowly drag the parameter to negative values until the object touches the ground)
The object starts to flicker while modifying the value.
5. Then drag the value back to positive numbers.
The object starts to flicker.

Pay close attention while reproducing. This flickering is not so obvious.

Reproduces with 5.6.0a6; 5.5.0f3; 5.4.3f1; 5.4.2f1; 5.4.0f3; 5.3.0f4; 5.2.0f3

Project with the bug is attached to this report.