By any chance is it also deleting the main record also?
It sounds like you have a cascading delete specfied in one or more relationship in Manage | Database | Relationships.
One possible scenario is that you enabled the "delete" option for both sides of a relationship between the layout's table and the portal's table (could be in a different set of occurrences than the ones specified for your layout and portal.) Deleting the portal records would then also delete the parent record and in turn that would delete all the other related records.
This is just one possible scenario. Other possible cascading delete's might produce this result. You'll need to review the relationships in your file by double clicking them and looking for these delete options to see if you can identify the one that needs to be removed so that this does not happen.
Thank you very much - this solved my problem