diff --git a/tests/AcDream.App.Tests/Rendering/PortalVisibilityBuilderTests.cs b/tests/AcDream.App.Tests/Rendering/PortalVisibilityBuilderTests.cs
index 38818c92..111b34ba 100644
--- a/tests/AcDream.App.Tests/Rendering/PortalVisibilityBuilderTests.cs
+++ b/tests/AcDream.App.Tests/Rendering/PortalVisibilityBuilderTests.cs
@@ -185,6 +185,32 @@ public class PortalVisibilityBuilderTests
         Assert.False(frame.OutsideView.IsEmpty);
     }
 
+    [Fact]
+    public void Build_ViewGrowthAfterDoneCell_RePopsGrownCell()
+    {
+        // Same A->B(near LEFT) + A->D(far RIGHT) + D->B(later) topology as
+        // Build_ViewGrowthAfterDoneCell_PropagatesNewSlicesToExit: B is popped via LEFT, then D grows B
+        // through RIGHT after B is done -> B re-pops. This is retail-faithful late growth (kept by the fix).
+        const uint A = 0x0001, B = 0x0002, D = 0x0003;
+        var a = Cell(A, new CellPortalInfo((ushort)B, 0, 0, 0), new CellPortalInfo((ushort)D, 1, 0, 0));
+        a.PortalPolygons.Add(QuadX(-0.9f, -0.3f, -2f));
+        a.PortalPolygons.Add(QuadX(0.3f, 0.9f, -5f));
+        var b = Cell(B, new CellPortalInfo((ushort)A, 0, 0, 0),
+                        new CellPortalInfo(0xFFFF, 1, 0, 0), new CellPortalInfo((ushort)D, 2, 0, 0));
+        b.PortalPolygons.Add(QuadX(-0.9f, -0.3f, -2f));
+        b.PortalPolygons.Add(QuadX(0.3f, 0.9f, -3f));
+        b.PortalPolygons.Add(QuadX(0.3f, 0.9f, -5f));
+        var d = Cell(D, new CellPortalInfo((ushort)B, 0, 0, 2));
+        d.PortalPolygons.Add(QuadX(0.3f, 0.9f, -5f));
+        var all = new Dictionary<uint, LoadedCell> { [A] = a, [B] = b, [D] = d };
+
+        var frame = Build(a, all);
+
+        // Membership (the flap-relevant output) is each cell once, regardless of re-pops.
+        Assert.Equal(new[] { B }, frame.OrderedVisibleCells.Where(c => c == B).ToArray());
+        Assert.Contains(D, frame.OrderedVisibleCells);
+    }
+
     [Fact]
     public void Builder_SealedCellar_NoExitPortal_OutsideViewEmpty()
     {