diff --git a/src/ZB.MOM.WW.ScadaBridge.CentralUI/Components/Pages/Deployment/InstanceConfigure.razor b/src/ZB.MOM.WW.ScadaBridge.CentralUI/Components/Pages/Deployment/InstanceConfigure.razor
index 6412f759..77497d9e 100644
--- a/src/ZB.MOM.WW.ScadaBridge.CentralUI/Components/Pages/Deployment/InstanceConfigure.razor
+++ b/src/ZB.MOM.WW.ScadaBridge.CentralUI/Components/Pages/Deployment/InstanceConfigure.razor
@@ -549,7 +549,7 @@
                                     @* Tri-state: blank = inherit the template alarm's flag.
                                        "Not reportable" is a real override, not a clear — it
                                        pins a reportable template alarm off for this instance. *@
-                                    <label class="form-label small text-uppercase text-muted fw-semibold mb-1">MES reportable</label>
+                                    <label class="form-label small text-uppercase text-muted fw-semibold mb-1">MES reportable override</label>
                                     <select class="form-select form-select-sm" data-test="alarm-mes-select" @bind="_editingMesReportableText">
                                         <option value="">Inherited (@(_editingAlarm.IsMesReportable ? "reportable" : "not reportable"))</option>
                                         <option value="true">Reportable</option>
@@ -1579,17 +1579,6 @@
         return parts.Count == 0 ? "(empty)" : string.Join(", ", parts);
     }
 
-    /// <summary>
-    /// The save-time delta rule: does the modal carry anything worth persisting?
-    /// When it does not, <see cref="SaveOverrideFromModal"/> DELETES any existing
-    /// override — so every override term must be represented here or it would be
-    /// silently dropped on save. A <c>false</c> MES-reportable choice counts: it
-    /// pins a reportable template alarm off for this instance, which is a real
-    /// override and not the same as inheriting.
-    /// </summary>
-    internal static bool HasOverrideDelta(string? overrideJson, int? priority, bool? mesReportable)
-        => !string.IsNullOrWhiteSpace(overrideJson) || priority.HasValue || mesReportable.HasValue;
-
     /// <summary>
     /// Opens the override editor modal pre-populated with the merged
     /// (inherited + existing override) config so the user sees the effective
diff --git a/src/ZB.MOM.WW.ScadaBridge.CentralUI/Components/Pages/Deployment/InstanceConfigure.razor.cs b/src/ZB.MOM.WW.ScadaBridge.CentralUI/Components/Pages/Deployment/InstanceConfigure.razor.cs
index 833ec62d..d3177571 100644
--- a/src/ZB.MOM.WW.ScadaBridge.CentralUI/Components/Pages/Deployment/InstanceConfigure.razor.cs
+++ b/src/ZB.MOM.WW.ScadaBridge.CentralUI/Components/Pages/Deployment/InstanceConfigure.razor.cs
@@ -115,6 +115,17 @@ public partial class InstanceConfigure
         return new CsvOverrideImportOutcome(overrides, Array.Empty<string>());
     }
 
+    /// <summary>
+    /// The save-time delta rule for the alarm-override modal: does it carry anything
+    /// worth persisting? When it does not, <c>SaveOverrideFromModal</c> DELETES any
+    /// existing override — so every override term must be represented here or it
+    /// would be silently dropped on save. A <c>false</c> MES-reportable choice
+    /// counts: it pins a reportable template alarm off for this instance, which is a
+    /// real override and not the same as inheriting.
+    /// </summary>
+    internal static bool HasOverrideDelta(string? overrideJson, int? priority, bool? mesReportable)
+        => !string.IsNullOrWhiteSpace(overrideJson) || priority.HasValue || mesReportable.HasValue;
+
     /// <summary>
     /// One validated native-alarm-source retarget from an imported CSV: the source
     /// binding's name plus the three optional override fields (null = keep the
diff --git a/tests/ZB.MOM.WW.ScadaBridge.CentralUI.PlaywrightTests/Deployment/InstanceConfigureTests.cs b/tests/ZB.MOM.WW.ScadaBridge.CentralUI.PlaywrightTests/Deployment/InstanceConfigureTests.cs
index ef603199..9e391a5c 100644
--- a/tests/ZB.MOM.WW.ScadaBridge.CentralUI.PlaywrightTests/Deployment/InstanceConfigureTests.cs
+++ b/tests/ZB.MOM.WW.ScadaBridge.CentralUI.PlaywrightTests/Deployment/InstanceConfigureTests.cs
@@ -527,7 +527,9 @@ public sealed class InstanceConfigureTests : IClassFixture<InstanceConfigureFixt
     /// priority DELETES the override, so a reportable-only choice has to count as a delta on its own
     /// or it would be silently dropped. The assertion is therefore that choosing ONLY "Reportable"
     /// (leaving the trigger config and priority untouched) creates the override — badge + a summary
-    /// naming <c>mesReportable</c> — and that switching back to Inherited removes it again.
+    /// naming <c>mesReportable</c> — that switching to "Not reportable" persists <c>false</c>
+    /// (verified against the read-back document, since an absent/null field there would mean the
+    /// negative pin was dropped), and that switching back to Inherited removes the override again.
     /// </para>
     ///
     /// <para>
@@ -563,6 +565,31 @@ public sealed class InstanceConfigureTests : IClassFixture<InstanceConfigureFixt
             // Summary part is "mesReportable" (the negative pin renders "notMesReportable").
             await Assertions.Expect(row).ToContainTextAsync("mesReportable", new() { Timeout = 15_000 });
 
+            // Reopen → switch to the NEGATIVE pin. This is the leg that proves "Not reportable" is
+            // a real write and not a clear: the row must stay overridden and the persisted
+            // isMesReportableOverride must be JSON false, never absent/null.
+            await row.Locator("[data-test='alarm-edit-btn']").ClickAsync();
+            await Assertions.Expect(mesSelect).ToBeVisibleAsync(new() { Timeout = 15_000 });
+            await mesSelect.SelectOptionAsync("false");
+            await page.Locator("[data-test='alarm-save-override']").ClickAsync();
+
+            await Assertions.Expect(row.Locator("[data-test='alarm-override-badge']"))
+                .ToBeVisibleAsync(new() { Timeout = 15_000 });
+            await Assertions.Expect(row).ToContainTextAsync("notMesReportable", new() { Timeout = 15_000 });
+
+            using (var negDoc = await CliRunner.GetInstanceDocumentAsync(_cfg.InstanceId))
+            {
+                var negOverrides = negDoc.RootElement.GetProperty("alarmOverrides");
+                var entry = negOverrides.EnumerateArray().Single(o =>
+                    o.GetProperty("alarmCanonicalName").GetString() == _cfg.AlarmName);
+
+                Assert.True(entry.TryGetProperty("isMesReportableOverride", out var flag),
+                    "alarmOverrides entry is missing isMesReportableOverride.");
+                // JSON false specifically — an absent/null field would mean the negative pin was
+                // dropped and the alarm silently fell back to the template's flag.
+                Assert.Equal(JsonValueKind.False, flag.ValueKind);
+            }
+
             // Reopen → back to Inherited (blank) → Save. With nothing else set that is now a
             // no-delta save, which clears the override outright.
             await row.Locator("[data-test='alarm-edit-btn']").ClickAsync();
diff --git a/tests/ZB.MOM.WW.ScadaBridge.CentralUI.Tests/Deployment/InstanceConfigureMesReportableTests.cs b/tests/ZB.MOM.WW.ScadaBridge.CentralUI.Tests/Deployment/InstanceConfigureMesReportableTests.cs
index 5dafbfff..a5ce1365 100644
--- a/tests/ZB.MOM.WW.ScadaBridge.CentralUI.Tests/Deployment/InstanceConfigureMesReportableTests.cs
+++ b/tests/ZB.MOM.WW.ScadaBridge.CentralUI.Tests/Deployment/InstanceConfigureMesReportableTests.cs
@@ -46,6 +46,9 @@ public class InstanceConfigureMesReportableTests
         var selectEnd = markup.IndexOf("</select>", selectStart, StringComparison.Ordinal);
         Assert.True(selectEnd > selectStart, "MES reportable select is not closed.");
 
+        // Label mirrors the adjacent "Priority override" control.
+        Assert.Contains("MES reportable override</label>", markup);
+
         var selectBody = markup[selectStart..selectEnd];
         var optionCount = selectBody.Split("<option").Length - 1;
         Assert.Equal(3, optionCount);