Secondary related data in a portal - a conundrum

[IdealData]

Recently I helped another forum member with an IWP issue and related images.

The attachment simplifies the problem to help analyse why IWP portals can't display graphics from a secondary relationship.

My sample has three tables, TableA, TableB, TableC. Each table is linked in a chain A --> B --> C so that a layout based on TableA can use related data from TableB and also include secondary related data from TableC.

I agree this is against all the rules for data in a portal (but technically it should work), however the relationship and portal works in FMP, but the IWP version cannot display the graphic from TableC, even though it can display a text field from TableC.

I'm not asking you to fix the problem as I can do that, but the challenge is to explain the different behaviour between FMP and IWP.

Relationships.fp7.zip

[IdealData]

Does any one have any ideas?