To reproduce:
1. Open scene 'Untitled' in attached project, drag 'GameObject' to hierarchy.
2. Observe that Unity crashes, when trying to change any rigidBody property in OnValidate, doesn't matter whether accessing it directly or via GetComponent<T>.
3. Doesn't crash when changing properties/variables on other components( Colliders & Custom scripts).

In 4.3 the behaviour is different, instead of crashing these, errors are thrown:
'm_Actor == NULL'
'ExecutionEngineException: SIGILL'

this only happens when modifying rigidbody props aswell and Unity freezes some times (when adding the object).