Editor values not updating in OnSceneGUI

So, here's my basic problem. My custom editor is using both OnInspectorGUI and OnSceneGUI.

The editor itself has several values - mostly integers - for holding editor state information. Things like which tab is selected, or which options in a list, things like that. When those values are updated, OnSceneGUI reports no change in them. Here is a simplified version:

 public class ProblemFinder : MonoBehaviour {
 
     // Tried containing variables on editor target, instead of editor, but got the same result.
     // public int testInt = -1;
     // public string[] testButtons = new string[] { "Test 1", "Bob", "Blueberry" };
 }
 
 
 [CustomEditor (typeof(ProblemFinder))]
 public class ProblemFinderEditor : Editor {
 
     int testInt = -1, currentInt = -1;
     string[] testButtons = new string[] { "Test 1", "Bob", "Blueberry" };
 
     public override void OnInspectorGUI()
     {
         Debug.Log("Test Int Value: " + testInt.ToString());
         for (int i = 0; i < testButtons.Length; i++)
         {
             
             if (currentInt != i && GUILayout.Button(testButtons[i]))
             {
                 testInt = i;
                 Debug.Log("Clicked " + testInt.ToString() + ". " + testButtons[i]);
                 SceneView.RepaintAll();
             }
             else if(currentInt ==i)
             {
                 GUILayout.Label(testButtons[i]);
             }
         }
     }
 
     public void OnSceneGUI()
     {
         Debug.Log("Scene View Updated: " + testInt.ToString());
         if (testInt != -1)
         {
             // I never see this message.  testInt ALWAYS == -1 in this function
             Debug.Log("Test Int = " + testInt.ToString());
             currentInt = testInt;
             testInt = -1;
         }
     }
 }

I see the three buttons I would expect, in the Inspector: Test 1, Bob, and Blueberry.

Clicking Blueberry returns the following:

Clicked 2. Blueberry

Scene View Updated: -1

My initial debug comment, in OnInspectorGUI confirms that testInt HOLDS its value of 2.

Even so, OnSceneGUI ALWAYS returns it with a value of -1. Anyone have any idea why?

I'm using Unity 5.5. I was not having this problem prior to updating, and some, but not all, other teammates, also now updated to 5.5 are NOT having the same issues.

I have tried reimporting the scripts, I've tried creating the test scripts above (which DO exhibit the exact issues I describe here), I've tried reinstalling Unity - and none of that has made an impact so far.