To Reproduce:

1. Open scene TrapWorkshop in the attached project.
2. Play, click on the sphere.
3. When it touches the plane click on it again.
4. Observe that even if the motor is turned on sometimes it doesn't work and sometimes disabling it in editor actually activates it.
(See the attached video)

Could only reproduce this in editor, more or less random, but seems to happen a bit more often after deactivating/activating game view.