Reporting Services Binding Related Object Fields

After upgrading my SSRS reports in VS2010, several of the expression fields are now broken.  For instance, using a data set of OrderItem, which contains standard order lines, I can access the fields directly represented by that object (the object structure was built using LINQ).  

However, related data cannot be so easily accessed.  Consider a inventory object contained-in the order line (related-to in the underlying database).  The inventory object is called OrderItemType, and I want to print out the description on each order line.  Sounds easy enough...

Before upgrading the following expression did in fact report the description from the related data:

=Fields!OrderItemType.Value.Description

However, now the "Description" portion is red-lined in the Expression editor, and when I run the report, it shows only "#VALUE" in the description field.

So what gives?  Did something change after the report upgrade that now requires a different syntax?  How can I once again print the description from the related table?

=Fields!OrderItemType.Value.Description

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