Why did this work in 5.2.1 but not in 5.2.3?

var intReader = Isolate.Fake.Instance<IRecordsReader>();
            Isolate.WhenCalled(() => intReader.GetDbType()).WillReturn("Integer");

            var ntextReader = Isolate.Fake.Instance<IRecordsReader>();
            Isolate.WhenCalled(() => ntextReader.GetDbType()).WillReturn("Ntext");

DocTypeObjectBuilder target = new DocTypeObjectBuilder(string.Empty);
            var intProp = target.BuildProperty(intReader);
            var ntextProp = target.BuildProperty(ntextReader);

Assert.AreEqual(typeof(int), intProp.DatabaseType);
            Assert.AreEqual(typeof(string), ntextProp.DatabaseType);