diff --git a/src/ScadaLink.CentralUI/Components/Shared/TreeView.razor b/src/ScadaLink.CentralUI/Components/Shared/TreeView.razor
index de894d5..6149e8c 100644
--- a/src/ScadaLink.CentralUI/Components/Shared/TreeView.razor
+++ b/src/ScadaLink.CentralUI/Components/Shared/TreeView.razor
@@ -104,6 +104,12 @@ else
                 ApplyInitialExpansion(_items);
             }
         }
+
+        // Clear selection if the selected key no longer exists in the current items tree
+        if (Selectable && SelectedKey != null && _items is not null && !KeyExistsInTree(_items, SelectedKey))
+        {
+            _ = SelectedKeyChanged.InvokeAsync(null);
+        }
     }
 
     protected override async Task OnAfterRenderAsync(bool firstRender)
@@ -133,6 +139,20 @@ else
         }
     }
 
+    private bool KeyExistsInTree(IReadOnlyList<TItem> items, object key)
+    {
+        foreach (var item in items)
+        {
+            if (key.Equals(KeySelector(item)))
+                return true;
+
+            var children = ChildrenSelector(item);
+            if (children is { Count: > 0 } && KeyExistsInTree(children, key))
+                return true;
+        }
+        return false;
+    }
+
     private void ApplyInitialExpansion(IReadOnlyList<TItem> items)
     {
         foreach (var item in items)
diff --git a/tests/ScadaLink.CentralUI.Tests/TreeViewTests.cs b/tests/ScadaLink.CentralUI.Tests/TreeViewTests.cs
index 4096b93..0f55d49 100644
--- a/tests/ScadaLink.CentralUI.Tests/TreeViewTests.cs
+++ b/tests/ScadaLink.CentralUI.Tests/TreeViewTests.cs
@@ -464,6 +464,119 @@ public class TreeViewTests : BunitContext
         Assert.Equal(2, labels.Count);
     }
 
+    // ── External filtering tests (R8) ──────────────────────────────────
+
+    [Fact]
+    public void Filtering_ReducedItems_HidesRemovedRoots()
+    {
+        var fullItems = SimpleRoots();
+        var cut = RenderTreeView(items: fullItems);
+
+        // Both roots visible
+        var labels = cut.FindAll(".node-label");
+        Assert.Equal(2, labels.Count);
+
+        // Re-render with only Alpha (Beta removed)
+        var alphaOnly = new List<TestNode> { fullItems[0] };
+        cut.Render(parameters =>
+        {
+            parameters
+                .Add(p => p.Items, alphaOnly)
+                .Add(p => p.ChildrenSelector, (Func<TestNode, IReadOnlyList<TestNode>>)(n => n.Children))
+                .Add(p => p.HasChildrenSelector, (Func<TestNode, bool>)(n => n.Children.Count > 0))
+                .Add(p => p.KeySelector, (Func<TestNode, object>)(n => n.Key))
+                .Add(p => p.NodeContent, (RenderFragment<TestNode>)(node => builder =>
+                {
+                    builder.AddMarkupContent(0, $"<span class=\"node-label\">{node.Label}</span>");
+                }));
+        });
+
+        labels = cut.FindAll(".node-label");
+        Assert.Single(labels);
+        Assert.Equal("Alpha", labels[0].TextContent);
+    }
+
+    [Fact]
+    public void Filtering_ExpansionStatePreserved()
+    {
+        var fullItems = SimpleRoots();
+        var cut = RenderTreeView(items: fullItems);
+
+        // Expand Alpha
+        cut.Find(".tv-toggle").Click();
+        Assert.Contains(cut.FindAll(".node-label"), l => l.TextContent == "Alpha-1");
+
+        // Re-render with only Alpha
+        var alphaOnly = new List<TestNode> { fullItems[0] };
+        cut.Render(parameters =>
+        {
+            parameters
+                .Add(p => p.Items, alphaOnly)
+                .Add(p => p.ChildrenSelector, (Func<TestNode, IReadOnlyList<TestNode>>)(n => n.Children))
+                .Add(p => p.HasChildrenSelector, (Func<TestNode, bool>)(n => n.Children.Count > 0))
+                .Add(p => p.KeySelector, (Func<TestNode, object>)(n => n.Key))
+                .Add(p => p.NodeContent, (RenderFragment<TestNode>)(node => builder =>
+                {
+                    builder.AddMarkupContent(0, $"<span class=\"node-label\">{node.Label}</span>");
+                }));
+        });
+
+        // Alpha-1 still visible (expansion state preserved)
+        Assert.Contains(cut.FindAll(".node-label"), l => l.TextContent == "Alpha-1");
+
+        // Re-render with full list again
+        cut.Render(parameters =>
+        {
+            parameters
+                .Add(p => p.Items, fullItems)
+                .Add(p => p.ChildrenSelector, (Func<TestNode, IReadOnlyList<TestNode>>)(n => n.Children))
+                .Add(p => p.HasChildrenSelector, (Func<TestNode, bool>)(n => n.Children.Count > 0))
+                .Add(p => p.KeySelector, (Func<TestNode, object>)(n => n.Key))
+                .Add(p => p.NodeContent, (RenderFragment<TestNode>)(node => builder =>
+                {
+                    builder.AddMarkupContent(0, $"<span class=\"node-label\">{node.Label}</span>");
+                }));
+        });
+
+        // Alpha-1 still visible after restoration
+        Assert.Contains(cut.FindAll(".node-label"), l => l.TextContent == "Alpha-1");
+    }
+
+    [Fact]
+    public void Filtering_SelectionCleared_WhenNodeDisappears()
+    {
+        var fullItems = SimpleRoots();
+        object? lastSelected = "b"; // track the last value passed to callback
+        var cut = RenderTreeView(
+            items: fullItems,
+            selectable: true,
+            selectedKey: "b",
+            onSelectedKeyChanged: k => lastSelected = k);
+
+        // Re-render with only Alpha (Beta disappears)
+        var alphaOnly = new List<TestNode> { fullItems[0] };
+        cut.Render(parameters =>
+        {
+            parameters
+                .Add(p => p.Items, alphaOnly)
+                .Add(p => p.ChildrenSelector, (Func<TestNode, IReadOnlyList<TestNode>>)(n => n.Children))
+                .Add(p => p.HasChildrenSelector, (Func<TestNode, bool>)(n => n.Children.Count > 0))
+                .Add(p => p.KeySelector, (Func<TestNode, object>)(n => n.Key))
+                .Add(p => p.NodeContent, (RenderFragment<TestNode>)(node => builder =>
+                {
+                    builder.AddMarkupContent(0, $"<span class=\"node-label\">{node.Label}</span>");
+                }))
+                .Add(p => p.Selectable, true)
+                .Add(p => p.SelectedKey, (object?)"b")
+                .Add(p => p.SelectedKeyChanged, (Action<object?>)(k => lastSelected = k));
+        });
+
+        // SelectedKeyChanged should have been called with null
+        Assert.Null(lastSelected);
+    }
+
+    // ── Context menu tests ──────────────────────────────────────────────
+
     [Fact]
     public void ContextMenu_Null_NoMenuRendered()
     {