To reproduce:
- Open attached "EditorGUILayout.unitypackage" and launch "test" scene
- In the top menu bar, go to "Test" and open the "popup Test" window
- Observe that no matter what index your are selecting on the window, only one "test" item is displayed in the drop down menu

User writes the following:

"The "Selected Index" is initialized to the middle of the list of options (all named "test"). If you play with changing the selected index you will see that the popup only ever shows a single row "test". The vertical positioning, however, appears to be calculated based on the selected index passed into the list.

The expected behavior is that the list shows all options; that it does not collapse duplicate entries."