diff --git a/src/ZB.MOM.WW.ScadaBridge.CentralUI/Components/Pages/Deployment/DebugTreeBuilder.cs b/src/ZB.MOM.WW.ScadaBridge.CentralUI/Components/Pages/Deployment/DebugTreeBuilder.cs
index e746d423..42dc7ec8 100644
--- a/src/ZB.MOM.WW.ScadaBridge.CentralUI/Components/Pages/Deployment/DebugTreeBuilder.cs
+++ b/src/ZB.MOM.WW.ScadaBridge.CentralUI/Components/Pages/Deployment/DebugTreeBuilder.cs
@@ -21,6 +21,13 @@ public static class DebugTreeBuilder
     /// <see cref="AttributeValueChanged.AttributeName"/>). Null/empty/whitespace
     /// keeps everything; matching leaves carry along their ancestor branches.
     /// </param>
+    /// <remarks>
+    /// The caller is expected to pass at most one <see cref="AttributeValueChanged"/>
+    /// per <see cref="AttributeValueChanged.AttributeName"/>. The DebugView page
+    /// enforces this by keying a dictionary on the attribute name before calling this
+    /// method. Passing duplicate names would produce sibling leaves with identical
+    /// keys under the same parent branch.
+    /// </remarks>
     public static IReadOnlyList<DebugTreeNode> BuildAttributeTree(
         IEnumerable<AttributeValueChanged> attributes, string? filter)
     {
@@ -71,7 +78,7 @@ public static class DebugTreeBuilder
         }
 
         SortAndRollUp(roots);
-        return roots;
+        return roots.AsReadOnly();
     }
 
     /// <summary>
diff --git a/tests/ZB.MOM.WW.ScadaBridge.CentralUI.Tests/Deployment/DebugTreeBuilderTests.cs b/tests/ZB.MOM.WW.ScadaBridge.CentralUI.Tests/Deployment/DebugTreeBuilderTests.cs
index 9ee4ce24..45aa2705 100644
--- a/tests/ZB.MOM.WW.ScadaBridge.CentralUI.Tests/Deployment/DebugTreeBuilderTests.cs
+++ b/tests/ZB.MOM.WW.ScadaBridge.CentralUI.Tests/Deployment/DebugTreeBuilderTests.cs
@@ -203,4 +203,33 @@ public class DebugTreeBuilderTests
         var tree = DebugTreeBuilder.BuildAttributeTree(Array.Empty<AttributeValueChanged>(), null);
         Assert.Empty(tree);
     }
+
+    [Fact]
+    public void RollUp_FourLevelDeepBadQuality_ReachesRoot()
+    {
+        var tree = DebugTreeBuilder.BuildAttributeTree(
+            new[] { Attr("A.B.C.D", quality: "Bad") }, null);
+
+        var a = Assert.Single(tree);
+        Assert.True(a.HasBadQuality);
+        var b = Assert.Single(a.Children);
+        Assert.True(b.HasBadQuality);
+        var c = Assert.Single(b.Children);
+        Assert.True(c.HasBadQuality);
+        var d = Assert.Single(c.Children);
+        Assert.True(d.HasBadQuality);
+    }
+
+    [Fact]
+    public void Filter_DeepLeafMatch_RetainsAllAncestorBranches()
+    {
+        var tree = DebugTreeBuilder.BuildAttributeTree(
+            new[] { Attr("Motor1.Compressor.Pump"), Attr("Motor1.Speed") }, "Pump");
+
+        var motor = Assert.Single(tree);
+        Assert.Equal("Motor1", motor.Key);
+        var compressor = Assert.Single(motor.Children);
+        Assert.Equal("Motor1.Compressor", compressor.Key);
+        Assert.Equal("Motor1.Compressor.Pump", Assert.Single(compressor.Children).Key);
+    }
 }