diff --git a/src/AcDream.App/UI/Layout/RetailTooltipPresenter.cs b/src/AcDream.App/UI/Layout/RetailTooltipPresenter.cs
index e58e6e9a..44f2d482 100644
--- a/src/AcDream.App/UI/Layout/RetailTooltipPresenter.cs
+++ b/src/AcDream.App/UI/Layout/RetailTooltipPresenter.cs
@@ -186,9 +186,34 @@ public sealed class RetailTooltipPresenter : IDisposable
     /// family resolves to). Extracted unchanged from the pre-#411-follow-on
     /// <c>OnTooltipShow</c> body — same F4/F5/F8 fixes, same failure
     /// handling.
+    ///
+    /// <para>
+    /// Night-round review F5: the single-popup invariant (retail's own
+    /// single <c>m_pTooltipElement</c> slot) is now enforced HERE,
+    /// structurally, rather than relying on every caller to have already
+    /// cleared a stale popup before reaching this method. Both existing
+    /// callers already clear on their own early-return paths too (a hover
+    /// change that resolves to no valid tooltip text must still tear down
+    /// the PREVIOUS popup, which never reaches this method at all), so
+    /// those calls stay — this is a belt-and-braces guarantee, not a
+    /// replacement for them. It closes a real hole: <see cref="UpdateWorldHoverTooltip"/>'s
+    /// own clear is gated on <c>_worldTooltipShowing</c> (only true when the
+    /// WORLD path itself mounted the current popup) and its "a UI popup
+    /// cannot be showing here" comment assumed <see cref="_host"/>'s hover
+    /// query is null whenever that branch runs — an assumption that does
+    /// not hold the instant a modal dialog opens over a stationary cursor:
+    /// the UI dwell popup from <see cref="OnTooltipShow"/> stays mounted
+    /// (<c>_owner</c>/<c>_popupRoot</c> set, <c>_worldTooltipShowing</c>
+    /// still false) while the world path could independently find an
+    /// object and call this method, mounting a second popup on top. Now it
+    /// cannot: this call clears whatever is mounted, UI-owned or
+    /// world-owned, before either ever gets a chance to layer.
+    /// </para>
     /// </summary>
     private bool TryBuildAndMountPopup(uint rootElementId, uint layoutDid, string tooltipText)
     {
+        RemovePopup();
+
         ImportedLayout? layout;
         try
         {
diff --git a/tests/AcDream.App.Tests/UI/Layout/RetailTooltipPresenterTests.cs b/tests/AcDream.App.Tests/UI/Layout/RetailTooltipPresenterTests.cs
index 0410533c..4cdc83a0 100644
--- a/tests/AcDream.App.Tests/UI/Layout/RetailTooltipPresenterTests.cs
+++ b/tests/AcDream.App.Tests/UI/Layout/RetailTooltipPresenterTests.cs
@@ -757,6 +757,58 @@ public sealed class RetailTooltipPresenterTests
         // childrenBefore world-target(none) + target(1) + popup(1) == +2 total,
         // never +3 (world popup replaced, not stacked).
         Assert.Equal(childrenBefore + 2, root.Children.Count);
+
+        // Night-round review F6: the test previously stopped here, which
+        // only proved OnTooltipShow's OWN unconditional RemovePopup()
+        // cleared the world popup — it never actually exercised what
+        // happens on the NEXT presenter.Tick() (UpdateWorldHoverTooltip
+        // still thinks a world-hover target exists, since its own
+        // _worldHoverGuid/_worldTooltipShowing bookkeeping was never
+        // re-evaluated after the transition). The mouse is now over the UI
+        // target, so Pick(...) finds it and WorldHoverGuidProvider is
+        // ignored (found=0u) — this must leave the UI popup exactly as-is,
+        // no incorrect extra removal or re-mount.
+        presenter.Tick();
+        Assert.Equal(childrenBefore + 2, root.Children.Count);
+        Assert.Same(popup, root.Children.Single(c => !ReferenceEquals(c, target)));
+    }
+
+    [Fact]
+    public void UiDwellTooltip_ThenModalStealsHitTesting_WorldHoverReplacesRatherThanStacks()
+    {
+        // Night-round review F5's own reproduction: the UI->world hole. A
+        // UI element's dwell tooltip is showing; a modal then opens WITHOUT
+        // the mouse moving (UiRoot.Modal claims EXCLUSIVE hit-testing —
+        // HitTestTopDown @0x... "Modal gets exclusive hit-test" — so
+        // Pick(MouseX, MouseY) now returns null even though the tooltip's
+        // owner widget is still mounted, still visible, and its popup is
+        // still up). UpdateWorldHoverTooltip's own clear is gated on
+        // _worldTooltipShowing, which is FALSE here (the currently-mounted
+        // popup is UI-owned, not world-owned) — pre-fix, this let the world
+        // path mount a SECOND popup on top without ever clearing the first.
+        var (root, presenter, _) = CreateHarness();
+        var target = AddFullyAuthoredTarget(root);
+        int childrenBefore = root.Children.Count;
+
+        root.OnMouseMove(110, 110);
+        root.Tick(0.016, 0);
+        root.Tick(0.016, root.TooltipDelayMs);
+        Assert.Equal(childrenBefore + 1, root.Children.Count); // UI tooltip up
+
+        // Modal opens elsewhere on screen, stealing exclusive hit-testing —
+        // the mouse never moves.
+        root.Modal = new UiPanel { Left = 0, Top = 0, Width = 10, Height = 10 };
+        presenter.WorldHoverGuidProvider = () => WorldFoundGuid;
+        presenter.WorldHoverNameResolver = _ => "A Drudge";
+        presenter.WorldTooltipsEnabled = () => true;
+
+        presenter.Tick();
+
+        // Exactly one popup (the world one, having replaced the UI one) —
+        // never two stacked.
+        Assert.Equal(childrenBefore + 1, root.Children.Count);
+        UiElement popup = root.Children.Single(c => !ReferenceEquals(c, target));
+        Assert.NotNull(popup);
     }
 
     [Fact]