Reproduction steps:
1. Open the attached project and open scene "test"
3. Select Cube
4. Notice that cube has two scripts ("test" and "EmptyScript") which both have "ExecuteInEditMode"
5. Disable EmptyScript script by checking flag in the inspector
6. Open script "EmptyScript" and delete line 7 "Void Start(){}
7. Notice that script is not working and there is no flag near the script in gameobject Cube to enable script again

Workaround: write an empty Start() function

Actual result: can not enable/disable script.
Expected result: ExecuteInEditMode should also have a checkbox near the script, for a testing reasons it is useful to enable/disable scripts.

reproduced on: 5.4.0b9, 5.3.3p2, 5.2.4f1