How to reproduce:

1. Open attached project
2. Open scene 1.unity
3. Play the scene
- Note how the Fixed and Hinge joints fall, while the Configurable joint stays put
- Reproduced in Version 5.4.0b7 (83df6fa5e23f), Version 5.3.2p4 (f3eb2e65f8a2), Version 5.2.4f1 (98095704e6fe)
- Workaround: use Configurable joint instead of Fixed or Hinge joints

- Won't Fix: Here the problem is that the connected bodies have mass ratios way above what PhysX's default solver can deal with. One can only count on ratios less than 10, with less reliability on below 100, but 1:5000 is just way above that as the test shows. ConfigurableJoint is only able to overcome the problem because of the projection flag exposed. This isn't a physical process and has downside of it's kind.