Microsoft WF .NET ExpressionText causes validation errors

Question

This is related to the Workflow Foundation .NET 4.0. We have found that when setting the ExpressionText to a reserved keyword such as "interface" or "class", the underlying Validation Service in the foundation throws a validation message stating "one or more children have validation errors or warnings".

We are setting the ExpressionText of an argument like this:

        Argument inArg = Argument.Create(typeof(T), ArgumentDirection.In);

        inArg.Expression = new VisualBasicValue<T>
        {
            ExpressionText = selectedItem,
        };

        mp.SetValue(inArg); 

Any idea if this is a known issue, and how we can handle it?