I'm guessing that records created in portal 2 don't have a Product ID as they are not being selected from the dropdown list. You could filter portal 1 to only show records that have Product ID's.
In layout mode, double click the portal and check 'filter portal records'
Paste this, changing whats inside the () to your actual product id.
For portal 2 do the same but delete the "not"
There are other ways but this would be the quickest.
Thanks for the help
That seems to have stopped the problem from happening. Beginning to think that theres another way of getting the info i need onto the invoice rather than two portals!