[6.0] Flag all properties as not unknown when saving changes

Fixes #26330

Author: ajcvickers

Diff for: src/EFCore/ChangeTracking/Internal/InternalEntityEntry.cs

@@ -1436,6 +1436,7 @@ public void AcceptChanges()
             }
 
             _stateData.FlagAllProperties(EntityType.PropertyCount(), PropertyFlag.IsTemporary, false);
+            _stateData.FlagAllProperties(EntityType.PropertyCount(), PropertyFlag.Unknown, false);
 
             var currentState = EntityState;
             if ((currentState == EntityState.Unchanged)

Diff for: test/EFCore.Specification.Tests/GraphUpdates/GraphUpdatesTestBase.cs

@@ -434,6 +434,10 @@ protected override void OnModelCreating(ModelBuilder modelBuilder, DbContext con
                             b => b.HasKey("OwnerWithKeyedCollectionId", "PrivateKey"));
                     });
 
+                modelBuilder
+                    .Entity<OwnerWithNonCompositeOwnedCollection>()
+                    .OwnsMany(e => e.Owned, owned => owned.HasKey("Id"));
+
                 modelBuilder.Entity<OwnerNoKeyGeneration>(
                     b =>
                     {
@@ -3287,6 +3291,35 @@ public string Bar
             }
         }
 
+        protected class OwnerWithNonCompositeOwnedCollection : NotifyingEntity
+        {
+            private int _id;
+            private ICollection<NonCompositeOwnedCollection> _owned = new ObservableHashSet<NonCompositeOwnedCollection>();
+
+            public int Id
+            {
+                get => _id;
+                set => SetWithNotify(value, ref _id);
+            }
+
+            public ICollection<NonCompositeOwnedCollection> Owned
+            {
+                get => _owned;
+                set => SetWithNotify(value, ref _owned);
+            }
+        }
+
+        protected class NonCompositeOwnedCollection : NotifyingEntity
+        {
+            private string _foo;
+
+            public string Foo
+            {
+                get => _foo;
+                set => SetWithNotify(value, ref _foo);
+            }
+        }
+
         protected class OwnerNoKeyGeneration : NotifyingEntity
         {
             private int _id;

Diff for: test/EFCore.Specification.Tests/GraphUpdates/GraphUpdatesTestBaseMiscellaneous.cs

@@ -296,6 +296,59 @@ await ExecuteWithStrategyInTransactionAsync(
                 });
         }
 
+        [ConditionalTheory] // Issue #26330
+        [InlineData(false)]
+        [InlineData(true)]
+        public virtual async Task Saving_unknown_key_value_marks_it_as_unmodified(bool async)
+        {
+            await ExecuteWithStrategyInTransactionAsync(
+                async context =>
+                    {
+                        var owner = new OwnerWithNonCompositeOwnedCollection();
+                        owner.Owned.Add(new() { Foo = "Milan" });
+
+                        if (async)
+                        {
+                            await context.AddAsync(owner);
+                            await context.SaveChangesAsync();
+                        }
+                        else
+                        {
+                            context.Add(owner);
+                            context.SaveChanges();
+                        }
+
+                        owner.Owned.Remove(owner.Owned.Single());
+                        owner.Owned.Add(new() { Foo = "Rome" });
+
+                        if (Fixture.ForceClientNoAction)
+                        {
+                            await Assert.ThrowsAsync<InvalidOperationException>(
+                                async () =>
+                                    _ = async
+                                        ? await context.SaveChangesAsync()
+                                        : context.SaveChanges());
+                        }
+                        else
+                        {
+                            _ = async
+                                ? await context.SaveChangesAsync()
+                                : context.SaveChanges();
+                        }
+                    },
+                async context =>
+                    {
+                        if (!Fixture.ForceClientNoAction)
+                        {
+                            var owner = async
+                                ? await context.Set<OwnerWithNonCompositeOwnedCollection>().SingleAsync()
+                                : context.Set<OwnerWithNonCompositeOwnedCollection>().Single();
+
+                            Assert.Equal("Rome", owner.Owned.Single().Foo);
+                        }
+                    });
+        }
+
         [ConditionalTheory] // Issue #19856
         [InlineData(false)]
         [InlineData(true)]

Diff for: test/EFCore.SqlServer.FunctionalTests/GraphUpdates/GraphUpdatesSqlServerOwnedTest.cs

@@ -454,6 +454,10 @@ protected override void OnModelCreating(ModelBuilder modelBuilder, DbContext con
                             b => b.HasKey("OwnerWithKeyedCollectionId", "PrivateKey"));
                     });
 
+                modelBuilder
+                    .Entity<OwnerWithNonCompositeOwnedCollection>()
+                    .OwnsMany(e => e.Owned, owned => owned.HasKey("Id"));
+
                 modelBuilder.Entity<OwnerNoKeyGeneration>(
                     b =>
                     {