To reproduce:
1. Open attached project (in 5.4 and older versions use testProject.unitypackage);
2. Open "Scene1" scene (in 5.4 and older versions use "test" scene);
3. Add "SteamVR_Camera" script to the Main Camera (Assets > SteamVR > Scripts > SteamVR_Camera);
4. Press "Expand" button (Look to the inspector when the Main Camera is chosen);
5. Press CTRL + Z until Editor crashes.

Expected result: Editor does not crash when reverting changes.
Actual result: Editor crashes when undoing changes.

Reproduced on versions: 5.2.5f1, 5.3.5f1, 5.4.5f1, 5.5.2p2, 2017.1.0a3, 5.6.0f1.