Isolate.Verify.NonPublic.WasCalled not working?

Hello I have an litte problem.
I could not get Isolate.Verify.NonPublic.WasCalled working as expected.

My Testcase:

[TestMethod]
        [Isolated]
        public void SaveStatusFullTest()
        {
            BaseEntityForTest<EntityIdKey> target = new BaseEntityForTest<EntityIdKey>(new EntityIdKey(123));
            PrivateObject privateObject = new PrivateObject(target, new PrivateType(typeof(BaseEntity<EntityIdKey>)));
            BaseEntity_Accessor<EntityIdKey> accessor = new BaseEntity_Accessor<EntityIdKey>(privateObject);
            target.TestValue = "Status Full Test";
            accessor._originalValues = new SortedList<string> { { "TestValue", "Ein alter Wert" } };
            accessor.State = EntityState.Full;
            Isolate.NonPublic.WhenCalled(DatabaseAccess_Accessor.ShadowedType.ReferencedType, "UpdateDatabaseObject").IgnoreCall();
            target.Save();
            Isolate.Verify.NonPublic.WasCalled(DatabaseAccess_Accessor.ShadowedType.ReferencedType, "UpdateDatabaseObject");
            Isolate.Verify.NonPublic.WasNotCalled(DatabaseAccess_Accessor.ShadowedType.ReferencedType, "InsertDatabaseObject");
            Assert.AreEqual(EntityState.Full, target.State);
            Assert.AreEqual("Status Full Test", target.TestValue);
            Assert.AreEqual("Status Full Test", accessor._originalValues["TestValue"]);
        }

DatabaseAccess is an internal static class so I used the Accessor to get the type.

target.Save(); calls DatabaseAccess.UpdateDatabaseObject();

Isolate.NonPublic.WhenCalled(DatabaseAccess_Accessor.ShadowedType.ReferencedType, "UpdateDatabaseObject").IgnoreCall() is working fine when replaced with an DoInstead this is also working fine.

Isolate.Verify.NonPublic.WasCalled(DatabaseAccess_Accessor.ShadowedType.ReferencedType, "UpdateDatabaseObject") always failes

Does anyone know the reason?

Regards
Michael