Purchase Orders

I've noticed that if we fill in the Work order/sales order fields after creating a purchase order that when we then look at the item we just purchased it does not reflect in the Quantities section on the main tab that there is anything on a Purchase order.  If I leave those fields blank it DOES show up but then we can't view the sales order/work order from the PO, which is something I like to be able to do.  Why can't we have it all?  Is there a setting I'm missing somewhere that allows us to have it all?