How to reproduce:
1. Open the attached project ("case_1153558-WrongAsmdef.zip")
2. Inspect the "NewAssembly" assembly definition in the Assets folder
3. Add an assembly definition reference by clicking the "+" button
4. Select any assembly definition from the list by clicking on it or by using the arrow keys
5. Notice how the selected reference is actually reflected in the inspector
6. Click Enter and edit the same assembly definition reference again
7. Notice that only the first selected assembly definition is saved as selected

Expected results: Selected assembly definition reference changes based on what is actually selected
Actual results: Selected assembly definition reference gets stuck on the first selection

Reproducible with: 2019.1.0a2, 2019.1.3f1, 2019.2.0b2, 2019.3.0a2
Not reproducible with: 2017.4.27f1, 2018.4.0f1, 2019.1.0a1