diff --git a/src/DynamicData.Tests/Cache/MergeManyChangeSetsCacheSourceCompareFixture.cs b/src/DynamicData.Tests/Cache/MergeManyChangeSetsCacheSourceCompareFixture.cs
index 54683c1c0..148e0ee04 100644
--- a/src/DynamicData.Tests/Cache/MergeManyChangeSetsCacheSourceCompareFixture.cs
+++ b/src/DynamicData.Tests/Cache/MergeManyChangeSetsCacheSourceCompareFixture.cs
@@ -52,9 +52,9 @@ public MergeManyChangeSetsCacheSourceCompareFixture()
     [Theory]
     [InlineData(5, 7)]
     [InlineData(10, 50)]
-#if false && !DEBUG
-    [InlineData(10, 1_000)]
+#if !DEBUG
     [InlineData(100, 100)]
+    [InlineData(10, 1_000)]
     [InlineData(1_000, 10)]
 #endif
     public async Task MultiThreadedStressTest(int marketCount, int priceCount)
diff --git a/src/DynamicData/Cache/Internal/FilterOnObservable.cs b/src/DynamicData/Cache/Internal/FilterOnObservable.cs
index 9c07397a7..ec2b77198 100644
--- a/src/DynamicData/Cache/Internal/FilterOnObservable.cs
+++ b/src/DynamicData/Cache/Internal/FilterOnObservable.cs
@@ -14,23 +14,19 @@ internal sealed class FilterOnObservable<TObject, TKey>(IObservable<IChangeSet<T
     private readonly Func<TObject, TKey, IObservable<bool>> _filterFactory = filterFactory ?? throw new ArgumentNullException(nameof(filterFactory));
     private readonly IObservable<IChangeSet<TObject, TKey>> _source = source ?? throw new ArgumentNullException(nameof(source));
 
-    public IObservable<IChangeSet<TObject, TKey>> Run() => _source.Transform((val, key) => new FilterProxy(val, _filterFactory(val, key)))
-                      .AutoRefreshOnObservable(proxy => proxy.FilterObservable, buffer, scheduler)
-                      .Filter(proxy => proxy.PassesFilter)
-                      .Transform(proxy => proxy.Value);
-
-    private sealed class FilterProxy
+    public IObservable<IChangeSet<TObject, TKey>> Run() =>
+        _source
+            .Transform((val, key) => new FilterProxy(val, _filterFactory(val, key)))
+            .AutoRefreshOnObservable(proxy => proxy.FilterObservable, buffer, scheduler)
+            .Filter(proxy => proxy.PassesFilter)
+            .TransformImmutable(proxy => proxy.Value);
+
+    private sealed class FilterProxy(TObject obj, IObservable<bool> observable)
     {
-        public FilterProxy(TObject obj, IObservable<bool> observable)
-        {
-            Value = obj;
-            FilterObservable = observable.DistinctUntilChanged().Do(filterValue => PassesFilter = filterValue);
-        }
-
-        public IObservable<bool> FilterObservable { get; }
-
-        public TObject Value { get; }
+        public TObject Value { get; } = obj;
 
         public bool PassesFilter { get; private set; }
+
+        public IObservable<bool> FilterObservable => observable.DistinctUntilChanged().Do(filterValue => PassesFilter = filterValue);
     }
 }
diff --git a/src/DynamicData/Cache/Internal/MergeManyCacheChangeSetsSourceCompare.cs b/src/DynamicData/Cache/Internal/MergeManyCacheChangeSetsSourceCompare.cs
index c7385735a..2d371ff08 100644
--- a/src/DynamicData/Cache/Internal/MergeManyCacheChangeSetsSourceCompare.cs
+++ b/src/DynamicData/Cache/Internal/MergeManyCacheChangeSetsSourceCompare.cs
@@ -71,7 +71,7 @@ public IObservable<IChangeSet<TDestination, TDestinationKey>> Run() => Observabl
                 .Subscribe();
 
             return new CompositeDisposable(shared.Connect(), subMergeMany, subParent);
-        }).Select(changes => changes.Transform(entry => entry.Child));
+        }).TransformImmutable(entry => entry.Child);
 
     private sealed class ParentChildEntry(TObject parent, TDestination child)
     {