To reproduce:
1. Open attached Unity project "GetBehaviours.zip"
2. Open "MyScene" scene
3. Click on "GameObject"
4. Inspect States (there should be names of all the states in the GameObject's Animator)
5. Click "Modify scene and save" button (it makes scene dirty and saves it through code) or do a change and save manually

Result: Upon saving the scene, Animator.GetBehaviours (MyScriptEditor.cs) does not return any states to the array (names list of States is empty)

Workaround: Clicking on "Reload scripts" or manually reloading the scripts fixes the bug

Reproduced on: 5.6.0f1, 5.6.4p1, 2017.1.2p2, 2017.2.0p1, 2017.3.0b8, 2018.1.0a3
Not reproduced on: 5.5.4p2, 5.6.0b9