Actually set the preference to unregistered

src/org/thoughtcrime/securesms/ApplicationPreferencesActivity.java

@@ -342,6 +342,7 @@ public class ApplicationPreferencesActivity extends PassphraseRequiredSherlockPr
                 break;
               case SUCCESS:
                 ((CheckBoxPreference)preference).setChecked(false);
+                TextSecurePreferences.setPushRegistered(ApplicationPreferencesActivity.this, false);
                 break;
             }
           }