Family / Part render material not working on catalog item based on parametric cell

I'm having real trouble getting render materials to show on catalog items I've created based on parametric cells (using the constraint / variable workflow). I've created:

a) A cell with a single cube in it, with OA_Length, OA_Width & OA_Height variables driving the geometry. I didn't assign a level nor a Family/Part in the cell itself, nor any catalog type.

b) A datagroup definition called "Equipment" containing the OA_Length, OA_Width & OA_Height properties for my equipment cube. 

c) A catalog type "Equipment" with property defs of "Equipment", "ObjectClassification", "ObjectDiscipline", "ObjectMaterial", "ObjectPhasing" and "ParaDef".

d) A catalog item "Electrical_Cube", with various default values entered as in the below example image:

e) A Family and a part (intend to make additional parts when this is working in principle), to drive the Level ("M-Volume") and render material. 

f) A material table and palette of various translucent materials for use to indicate equipment massing by discipline. 

I'm able to place these equipment cubes now using the AECOsim > Architectural > Object tool, and I can modify them parametrically on placement or after placement as intended.

The only thing which isn't working as expected is the render material isn't displaying. Before accepting the placement the blocks are grey, after acceptance they go purple (the colour of the M-Volume level), even though they have the right part assigned, and do show on the mouse tooltip and in their properties to have a material assignment...

Ultimately, I'm aiming to be able to place massing blocks of varying colour (dependent upon discipline), that can have their O/A dims amended via their properties, and which all can be tabulated within the schedules system. 

Currently the only way I can get the materials to show is by dropping the placed content twice (once dropping the "compound cell", and then dropping the "Parametric solid"). After I've done that, I can then assign the material in the normal way and it works. Another way I found is to assign material by level to the M-Volume level, but this won't be the behaviour I'm after. 

Any help / advice / pointers would be much appreciated.

(I'm running ABD CE Update 4)