diff --git a/src/ZB.MOM.WW.ScadaBridge.Commons/Types/Flattening/FlattenedConfiguration.cs b/src/ZB.MOM.WW.ScadaBridge.Commons/Types/Flattening/FlattenedConfiguration.cs
index b9fb2efd..6f468538 100644
--- a/src/ZB.MOM.WW.ScadaBridge.Commons/Types/Flattening/FlattenedConfiguration.cs
+++ b/src/ZB.MOM.WW.ScadaBridge.Commons/Types/Flattening/FlattenedConfiguration.cs
@@ -78,6 +78,17 @@ public sealed record ResolvedAttribute
     /// </summary>
     public string? DataSourceReference { get; init; }
 
+    /// <summary>
+    /// The data-source reference as resolved from the template chain BEFORE any
+    /// per-instance <c>InstanceConnectionBinding.DataSourceReferenceOverride</c> was
+    /// applied — i.e. the template/composed default the Configure page shows as the
+    /// placeholder. Equals <see cref="DataSourceReference"/> when no override is set;
+    /// null for attributes that are not data-sourced.
+    /// Central-side presentation data only: deliberately excluded from the revision
+    /// hash (<c>RevisionHashService</c> projects through <c>HashableAttribute</c>).
+    /// </summary>
+    public string? DefaultDataSourceReference { get; init; }
+
     /// <summary>
     /// If data-sourced: the resolved connection ID from the instance binding.
     /// </summary>
diff --git a/src/ZB.MOM.WW.ScadaBridge.TemplateEngine/Flattening/FlatteningService.cs b/src/ZB.MOM.WW.ScadaBridge.TemplateEngine/Flattening/FlatteningService.cs
index bf4fca32..c01e5be7 100644
--- a/src/ZB.MOM.WW.ScadaBridge.TemplateEngine/Flattening/FlatteningService.cs
+++ b/src/ZB.MOM.WW.ScadaBridge.TemplateEngine/Flattening/FlatteningService.cs
@@ -369,6 +369,15 @@ public class FlatteningService
         Dictionary<string, ResolvedAttribute> attributes,
         IReadOnlyDictionary<int, DataConnection> dataConnections)
     {
+        // Capture the pre-binding default for EVERY data-sourced attribute (bound or
+        // not) so the Configure page can show the template default as a placeholder.
+        foreach (var key in attributes.Keys.ToList())
+        {
+            var attr = attributes[key];
+            if (attr.DataSourceReference is not null && attr.DefaultDataSourceReference is null)
+                attributes[key] = attr with { DefaultDataSourceReference = attr.DataSourceReference };
+        }
+
         foreach (var binding in bindings)
         {
             if (!attributes.TryGetValue(binding.AttributeName, out var existing))
@@ -385,7 +394,8 @@ public class FlatteningService
                 BoundDataConnectionId = connection.Id,
                 BoundDataConnectionName = connection.Name,
                 BoundDataConnectionProtocol = connection.Protocol,
-                DataSourceReference = binding.DataSourceReferenceOverride ?? existing.DataSourceReference
+                DataSourceReference = binding.DataSourceReferenceOverride ?? existing.DataSourceReference,
+                DefaultDataSourceReference = existing.DefaultDataSourceReference ?? existing.DataSourceReference
             };
         }
     }
diff --git a/tests/ZB.MOM.WW.ScadaBridge.TemplateEngine.Tests/Flattening/DefaultDataSourceReferenceTests.cs b/tests/ZB.MOM.WW.ScadaBridge.TemplateEngine.Tests/Flattening/DefaultDataSourceReferenceTests.cs
new file mode 100644
index 00000000..1daf2b2d
--- /dev/null
+++ b/tests/ZB.MOM.WW.ScadaBridge.TemplateEngine.Tests/Flattening/DefaultDataSourceReferenceTests.cs
@@ -0,0 +1,81 @@
+using ZB.MOM.WW.ScadaBridge.Commons.Entities.Instances;
+using ZB.MOM.WW.ScadaBridge.Commons.Entities.Sites;
+using ZB.MOM.WW.ScadaBridge.Commons.Entities.Templates;
+using ZB.MOM.WW.ScadaBridge.Commons.Types.Enums;
+using ZB.MOM.WW.ScadaBridge.Commons.Types.Flattening;
+using ZB.MOM.WW.ScadaBridge.TemplateEngine.Flattening;
+
+namespace ZB.MOM.WW.ScadaBridge.TemplateEngine.Tests.Flattening;
+
+/// <summary>
+/// Design 2026-08-20 (grouped connection bindings): the flattened attribute
+/// carries the data-source reference as it was BEFORE the instance binding
+/// override, so the Configure page can show the template default next to the
+/// effective reference. The field is deliberately NOT part of the revision hash.
+/// </summary>
+public class DefaultDataSourceReferenceTests
+{
+    [Fact]
+    public void RevisionHash_IgnoresDefaultDataSourceReference()
+    {
+        var svc = new RevisionHashService();
+        var a = new ResolvedAttribute
+        {
+            CanonicalName = "LeftMESReceiver.MoveInFlag",
+            DataType = "Boolean",
+            DataSourceReference = "MESReceiver_022.MoveInFlag",
+            BoundDataConnectionId = 1
+        };
+        var without = new FlattenedConfiguration { InstanceUniqueName = "Z28061", Attributes = [a] };
+        var with = without with { Attributes = [a with { DefaultDataSourceReference = "MoveInFlag" }] };
+
+        Assert.Equal(svc.ComputeHash(without), svc.ComputeHash(with));
+    }
+
+    [Fact]
+    public void ResolvedAttribute_DefaultDataSourceReference_IsNullByDefault()
+    {
+        var a = new ResolvedAttribute { CanonicalName = "X" };
+        Assert.Null(a.DefaultDataSourceReference);
+    }
+
+    [Fact]
+    public void Flatten_PopulatesDefault_ForBoundAndUnboundDataSourcedAttributes()
+    {
+        var template = new Template("Base") { Id = 1 };
+        template.Attributes.Add(new TemplateAttribute("MoveInFlag") { DataType = DataType.Boolean, DataSourceReference = "MoveInFlag" });
+        template.Attributes.Add(new TemplateAttribute("Unbound") { DataType = DataType.Boolean, DataSourceReference = "UnboundRef" });
+        template.Attributes.Add(new TemplateAttribute("Static") { DataType = DataType.Boolean, Value = "false" });
+
+        var instance = new Instance("Z28061") { Id = 1, TemplateId = 1, SiteId = 1 };
+        instance.ConnectionBindings.Add(new InstanceConnectionBinding("MoveInFlag")
+        {
+            DataConnectionId = 1,
+            DataSourceReferenceOverride = "MESReceiver_022.MoveInFlag"
+        });
+
+        var connections = new Dictionary<int, DataConnection>
+        {
+            [1] = new("GW", "MxGateway", 1) { Id = 1, PrimaryConfiguration = "http://localhost" }
+        };
+
+        var result = new FlatteningService().Flatten(
+            instance,
+            [template],
+            new Dictionary<int, IReadOnlyList<TemplateComposition>>(),
+            new Dictionary<int, IReadOnlyList<Template>>(),
+            connections);
+
+        Assert.True(result.IsSuccess, result.IsFailure ? result.Error : null);
+        var bound = result.Value.Attributes.Single(a => a.CanonicalName == "MoveInFlag");
+        Assert.Equal("MESReceiver_022.MoveInFlag", bound.DataSourceReference);
+        Assert.Equal("MoveInFlag", bound.DefaultDataSourceReference);
+
+        var unbound = result.Value.Attributes.Single(a => a.CanonicalName == "Unbound");
+        Assert.Equal("UnboundRef", unbound.DataSourceReference);
+        Assert.Equal("UnboundRef", unbound.DefaultDataSourceReference);
+
+        var stat = result.Value.Attributes.Single(a => a.CanonicalName == "Static");
+        Assert.Null(stat.DefaultDataSourceReference);
+    }
+}