Unable to use multiple Identity Keys in a table with model driven development

I have a table in my model and I want it to have 4 integer primary keys (defaulted to 0). When I create a new entry in this table using DataServiceTransaction.createItem(), only the PK1 goes correctly, the rest go as the default value 0. I tried to change the type of PKs to string but to no avail. What may be going on?

Please note the IDs are not auto generated

-RK