Reproduction steps:
1. Open the attached project
2. Open the "test" scene
3. Notice that Cube gameobject has script which was deleted attached (missing (Mono Script))
4. Open the "Select MonoScript" window by clicking on the little circle near the script
5. Select "Second" script and then select "Third script"
6. Notice that "Second" script is selected and can not select other scripts

Note, additional to this issue, from 5.3.0 we can no longer change script with the same little circle near the script, might be related.

Reproduced on: 5.3.0f4, 5.3.5f1, 5.4.0b18
Could not reproduce on: 5.2.4f1