How to reproduce:
1. Open attached "repro_1046717" project
2. Select gameObject "GameObject" inside Hierarchy view
3. Take note that inside Inspector view Script component is called "Test (Script)"
4. Inside Project view move "Test.cs" script into "Editor" folder
5. Look at Inspector view again and notice that Script component is now called "Game Object (Object)"
6. Select "Main Camera" object inside Hierarchy view and then reselect gameObject "GameObject"
7. Again notice that Script component, depending on what version you are testing, is now called either "Nothing selected" or "(Script)"

Expected result: While trying to move Script into "Editor" folder user receives warning stating that: it is not allowed to move MonoBehaviour script in to Editor and by doing that user will break any gameObject with such script attached
Actual result: Script file is successfully moved into Editor folder, Console prints warning "Game Object (named 'GameObject') references runtime script in scene file. Fixing!" and inside Inspector view user gets warning that script file can not be loaded asking them to fix compile errors

Reproducible with: 2017.1.4p1, 2017.2.3p1, 2017.4.5f1, 2018.1.4f1, 2018.2.0b7, 2018.3.0a1

Note: Works the same with the prefabs inside project view