Updating sharepoint item multi lookup field via odata

I need some help sorting out some syntax for an update to a list item in sharepoint from an application. Here's a rundown on the situation :

There are two lists within this sp site. One list is a products list, and the second list is a pricing. The way these lists are setup however are a 1 to many scheme. One product can have many pricing records. The product then has a column against it that is a look up field that supports multiple values.

Using REST and oData I can query and get the pricing information easily enough now, but my problem is when I need to update the products record to add a price.

with regular lookup fields I normally just set the ID property for the object, then call the update and savechanges methods for that list. With the pricing column however supporting multiple records there is no ID to set, and the field is an array of sorts. Adding the pricing object (list item) and updating and savechanges doesn't actually save. No errors are thrown but the then when viewing the list it isn't actually saving.

How can I add a price lookup to my Product?

I wrote a small method to query through each price and add it's initial price to the product below for testing :

InventoryCatalogDataContext dc = new InventoryCatalogDataContext(_pushinTinSvc);
        dc.Credentials = CredentialCache.DefaultCredentials;

        List<PricingItem> pricing = (from q in dc.Pricing
                                     select q).ToList<PricingItem>();

        foreach (PricingItem price in pricing)
        {                
            var query = (DataServiceQuery<ProductsItem>)
                        dc.Products
                        .Expand("Pricing")
                        .Where(p => p.Id.Equals(price.StockCodeId));


            List<ProductsItem> prods = query.ToList<ProductsItem>();
            ProductsItem product = prods[0];

            product.Pricing.Add(price);
            dc.UpdateObject(product);
        }

        try
        {
            dc.SaveChanges();
        }
        catch (Exception ex)
        {
            string stopHere = ex.Message;
        }

I'm not sure if I'm doing something wrong or if this is a bug. If I inspect the item after the SaveChanges, the item still has the pricing item lookup attached, showing a count of 1. At the end of the code block, if I re-query for the product, at that point it even still has the pricing attached. But once the method finishes and returns to the UI, the pricing is no longer attached, the fields are empty when you look at the list in sharepoint, but the version does increment. So I'm a little lost...