Problem using WithExactArguments

I have a test structured as follows (uses typemock 6.0.6):

        [TestMethod, Isolated]
        public void PrintItemsControllerCreatePrintItem()
        {
            // Arrange
            var fakeDal = Isolate.Fake.Instance<Wlgore>();
            Isolate.Swap.AllInstances<Wlgore>().With(fakeDal);

            var fakeCn = Isolate.Fake.Instance<Oracle>();
            Isolate.Swap.AllInstances<Oracle>().With(fakeCn);

            Isolate.WhenCalled(() => fakeDal.GetQualificationItemNumbersAndFormats(fakeCn, FormatType.Box)).DoInstead(context => { return new ItemNumberFormatStub().GetDataReaderStub(); });
            Isolate.WhenCalled(() => fakeDal.GetFormats(fakeCn, FormatType.Box)).DoInstead(context => { return new FormatFileStub().GetDataReaderStub(); });
            //Isolate.WhenCalled(() => fakeDal.GetQualificationItemNumbers(fakeCn, FormatType.Box, @"\SomeServerSomeDirectoryBOX_FORMAT_1.FMT")).DoInstead(context => { return new SingleItemNumbersStub().GetDataReaderStub(); });
            Isolate.WhenCalled(() => fakeDal.GetQualificationItemNumbers(fakeCn, FormatType.Box, "\\SomeServer\SomeDirectory\BOX_FORMAT_1.FMT")).WithExactArguments().DoInstead(context => { return new SingleItemNumbersStub().GetDataReaderStub(); });
            Isolate.WhenCalled(() => fakeDal.GetQualificationItemNumbers(fakeCn, FormatType.Box, "\\SomeServer\SomeDirectory\BOX_FORMAT_2.FMT")).WithExactArguments().DoInstead(context => { return new ItemNumbersStub().GetDataReaderStub(); });
            Isolate.WhenCalled(() => fakeDal.GetQualificationItemPackageAttributes(fakeCn, "111")).DoInstead(context => { return new SingleItemPkgAttsStub().GetDataReaderStub(); });

            // Act
            var testObj = Wlgore.LQS.Library.PrintItemsController.GetController();
            testObj.FormatType = FormatType.Box;

            var newFormatFileFilter = testObj.FormatsFilterList[0].FormatFile;
            testObj.FormatFileFilter = newFormatFileFilter;

            var itemNumber = testObj.FilteredItemNumbers[0].ItemNumber;

However the last line throws an error as the FilteredItemNumbers list never gets populated by the mock call:

Isolate.WhenCalled(() => fakeDal.GetQualificationItemNumbers(fakeCn, FormatType.Box, "\\SomeServer\SomeDirectory\BOX_FORMAT_1.FMT")).WithExactArguments().DoInstead(context => { return new SingleItemNumbersStub().GetDataReaderStub(); });

The DoInstead call never executes. If the 'WithExactArguments' is removed then the test works as expected. Any pointers or clues as to the issue, would be appreciated.