diff --git a/src/ZB.MOM.WW.ScadaBridge.TemplateEngine/Flattening/DiffService.cs b/src/ZB.MOM.WW.ScadaBridge.TemplateEngine/Flattening/DiffService.cs
index 1182af78..d17bcfe5 100644
--- a/src/ZB.MOM.WW.ScadaBridge.TemplateEngine/Flattening/DiffService.cs
+++ b/src/ZB.MOM.WW.ScadaBridge.TemplateEngine/Flattening/DiffService.cs
@@ -119,6 +119,11 @@ public class DiffService
         a.CanonicalName == b.CanonicalName &&
         a.Value == b.Value &&
         a.DataType == b.DataType &&
+        // #290: ElementDataType is part of the revision hash, so the diff must
+        // treat a List element-type change (e.g. Int32 → Double) with identical
+        // JSON-encoded values as a Changed attribute — keeping the structured
+        // diff in parity with the staleness hash.
+        a.ElementDataType == b.ElementDataType &&
         a.Description == b.Description &&
         a.IsLocked == b.IsLocked &&
         a.DataSourceReference == b.DataSourceReference &&
diff --git a/src/ZB.MOM.WW.ScadaBridge.TemplateEngine/Flattening/RevisionHashService.cs b/src/ZB.MOM.WW.ScadaBridge.TemplateEngine/Flattening/RevisionHashService.cs
index 19337841..8bdc978d 100644
--- a/src/ZB.MOM.WW.ScadaBridge.TemplateEngine/Flattening/RevisionHashService.cs
+++ b/src/ZB.MOM.WW.ScadaBridge.TemplateEngine/Flattening/RevisionHashService.cs
@@ -53,6 +53,7 @@ public class RevisionHashService
                     CanonicalName = a.CanonicalName,
                     Value = a.Value,
                     DataType = a.DataType,
+                    ElementDataType = a.ElementDataType,
                     Description = a.Description,
                     IsLocked = a.IsLocked,
                     DataSourceReference = a.DataSourceReference,
@@ -174,6 +175,16 @@ public class RevisionHashService
         /// </summary>
         public string? Description { get; init; }
         /// <summary>
+        /// For List attributes: the element scalar type name; null otherwise.
+        /// Folded into the hash (#290) so a List element-type change (e.g.
+        /// Int32 → Double) with identical JSON-encoded values is detected as a
+        /// staleness/revision change. Null for scalar attributes — and because
+        /// the serializer ignores null properties
+        /// (<see cref="JsonIgnoreCondition.WhenWritingNull"/>), scalar-only
+        /// configurations hash identically to before this field was added.
+        /// </summary>
+        public string? ElementDataType { get; init; }
+        /// <summary>
         /// Whether the attribute is locked.
         /// </summary>
         public bool IsLocked { get; init; }
diff --git a/tests/ZB.MOM.WW.ScadaBridge.TemplateEngine.Tests/Flattening/DiffServiceTests.cs b/tests/ZB.MOM.WW.ScadaBridge.TemplateEngine.Tests/Flattening/DiffServiceTests.cs
index fb5fa89f..ef83f798 100644
--- a/tests/ZB.MOM.WW.ScadaBridge.TemplateEngine.Tests/Flattening/DiffServiceTests.cs
+++ b/tests/ZB.MOM.WW.ScadaBridge.TemplateEngine.Tests/Flattening/DiffServiceTests.cs
@@ -162,6 +162,37 @@ public class DiffServiceTests
         Assert.Equal(DiffChangeType.Changed, diff.AttributeChanges[0].ChangeType);
     }
 
+    [Fact]
+    public void ComputeDiff_AttributeElementDataTypeChange_DetectedAsChanged()
+    {
+        // #290: ElementDataType is part of the revision hash, so AttributesEqual
+        // must also compare it — a List element-type change (Int32 → Double) with
+        // identical JSON-encoded values must surface as a Changed attribute,
+        // keeping the structured diff in parity with the staleness hash.
+        var oldConfig = new FlattenedConfiguration
+        {
+            InstanceUniqueName = "Instance1",
+            Attributes =
+            [
+                new ResolvedAttribute { CanonicalName = "Readings", Value = "[1,2]", DataType = "List", ElementDataType = "Int32" }
+            ]
+        };
+        var newConfig = new FlattenedConfiguration
+        {
+            InstanceUniqueName = "Instance1",
+            Attributes =
+            [
+                new ResolvedAttribute { CanonicalName = "Readings", Value = "[1,2]", DataType = "List", ElementDataType = "Double" }
+            ]
+        };
+
+        var diff = _sut.ComputeDiff(oldConfig, newConfig);
+
+        Assert.True(diff.HasChanges);
+        Assert.Single(diff.AttributeChanges);
+        Assert.Equal(DiffChangeType.Changed, diff.AttributeChanges[0].ChangeType);
+    }
+
     [Fact]
     public void ComputeDiff_AlarmDescriptionChange_DetectedAsChanged()
     {
diff --git a/tests/ZB.MOM.WW.ScadaBridge.TemplateEngine.Tests/Flattening/RevisionHashServiceTests.cs b/tests/ZB.MOM.WW.ScadaBridge.TemplateEngine.Tests/Flattening/RevisionHashServiceTests.cs
index 0c13f8ff..93fd1323 100644
--- a/tests/ZB.MOM.WW.ScadaBridge.TemplateEngine.Tests/Flattening/RevisionHashServiceTests.cs
+++ b/tests/ZB.MOM.WW.ScadaBridge.TemplateEngine.Tests/Flattening/RevisionHashServiceTests.cs
@@ -279,6 +279,94 @@ public class RevisionHashServiceTests
         Assert.Equal(_sut.ComputeHash(config1), _sut.ComputeHash(config2));
     }
 
+    [Fact]
+    public void ComputeHash_ListElementDataTypeChange_ChangesHash()
+    {
+        // #290: a List attribute whose element type changes (Int32 → Double)
+        // while the JSON-encoded values stay identical MUST produce a different
+        // revision hash, so the deployment is flagged stale. ElementDataType is
+        // folded into the hashable projection precisely for this case.
+        var baseAttr = new ResolvedAttribute
+        {
+            CanonicalName = "Readings",
+            Value = "[1,2]",
+            DataType = "List",
+            ElementDataType = "Int32"
+        };
+        var editedAttr = baseAttr with { ElementDataType = "Double" };
+
+        var configBefore = new FlattenedConfiguration
+        {
+            InstanceUniqueName = "Instance1",
+            TemplateId = 1,
+            SiteId = 1,
+            Attributes = [baseAttr]
+        };
+        var configAfter = configBefore with { Attributes = [editedAttr] };
+
+        Assert.NotEqual(_sut.ComputeHash(configBefore), _sut.ComputeHash(configAfter));
+    }
+
+    [Fact]
+    public void ComputeHash_SameListElementDataType_SameHash()
+    {
+        // #290: two List attributes identical in every field — including
+        // ElementDataType — must hash the same.
+        var attr = new ResolvedAttribute
+        {
+            CanonicalName = "Readings",
+            Value = "[1,2]",
+            DataType = "List",
+            ElementDataType = "Int32"
+        };
+
+        var config1 = new FlattenedConfiguration
+        {
+            InstanceUniqueName = "Instance1",
+            TemplateId = 1,
+            SiteId = 1,
+            Attributes = [attr]
+        };
+        var config2 = config1 with { Attributes = [attr with { }] };
+
+        Assert.Equal(_sut.ComputeHash(config1), _sut.ComputeHash(config2));
+    }
+
+    [Fact]
+    public void ComputeHash_ScalarAttribute_NullVsUnsetElementDataType_SameHash()
+    {
+        // #290 no-op guard: a scalar attribute has a null ElementDataType, and
+        // the canonical serializer omits null properties
+        // (DefaultIgnoreCondition = WhenWritingNull). Explicitly setting
+        // ElementDataType = null must therefore hash identically to leaving it
+        // at its default — i.e. adding the field is a no-op for scalars and does
+        // not retroactively change their hashes.
+        var withExplicitNull = new ResolvedAttribute
+        {
+            CanonicalName = "Temperature",
+            Value = "25",
+            DataType = "Double",
+            ElementDataType = null
+        };
+        var withDefault = new ResolvedAttribute
+        {
+            CanonicalName = "Temperature",
+            Value = "25",
+            DataType = "Double"
+        };
+
+        var config1 = new FlattenedConfiguration
+        {
+            InstanceUniqueName = "Instance1",
+            TemplateId = 1,
+            SiteId = 1,
+            Attributes = [withExplicitNull]
+        };
+        var config2 = config1 with { Attributes = [withDefault] };
+
+        Assert.Equal(_sut.ComputeHash(config1), _sut.ComputeHash(config2));
+    }
+
     private static FlattenedConfiguration CreateConfig(string instanceName, string tempValue)
     {
         return new FlattenedConfiguration