Self-service Procurement Catalog mapping to Purchase Group

Hi, 
I am setting up Procurement portal with a Supplier. 
We are using OCI with this supplier. I get the punchout connection to work, and item is returned to basket.

I do however not see the category returned.
in the payload I can see that NEW_ITEM-MATGROUP[1] is 53102503. I would expect this value to be present in field Suppliers Part Category. 
Am I missing some setup or is this a bug?