Steps to reproduce :

- create a new project
- add a cube in the scene
- add Hinge Joint 2D and notice that you cannot write a negative number in Angle Limits
- download the script attached to the report and import it in the project
- attach the script to the cube
- Under Element 0 change the Limit Min to a negative number and notice it's changed in the Angle Limits aswell

Duplicate :
http://issuetracker.unity3d.com/issues/its-possible-to-change-a-hinge-joint-2d-motor-speed-to-a-negative-value-through-scripting