OnDestroy in Editor - memory loss issue

When a ExecuteInEditMode-script get the OnDestroy event when the I start debugging, all variables are empty. I want to be able to save the state of my editor when I start debugging.

 [ExecuteInEditMode] //Will make the script run in the editor
 public class TestEditorMemScript : MonoBehaviour {
     int? testval1;
 
     // Use this for initialization
     void Start () {
         testval1 = 1;
     }
 
     void OnDestroy()
     {
         print("test mem script destroyed");
         print("is playing " + Application.isPlaying.ToString());
         if (testval1 == null)
         {
             print("testvalue is NULL");
         }
     }
 }

This gets the following output when I start and exit the debugging

-test mem script destroyed

-is playing False

-testvalue is NULL

-test mem script destroyed

-is playing True

The problem only appears when going from editor- to play mode.

One obvious choice is to save each update, but it seems a bit unnecessary if there is a proper way to do it.