To reproduce:
1.Download and open attached project
2.Open "SimpleVoхelPack" folder
3.Go to scenes folder and open "Forest" Scene
4.Select any object from the scene except "ENVIRONMENT" object
5.Press revert button in the inspector
6.Press CTRL+Z to undo changes
7.Notice that 2 objects in the hierarchy with the same name are created
8.Select object which has the arrow to view its child objects and press that arrow

Reproduced with: 5.6.0b2, 5.5.0p3, 5.4.3p3, 5.3.7p2
Not reproduced with: 5.3.5f1, 5.2.5f1.

Expected result: Changes are reverted without additional object and Unity does not crash.
Actual result: Changes are reverted with additional object and editing this object causes editor to crash.

Note: bug only occurs when prefab connection of that model is broken.