That highlight is intended to tell the user that they have selected the record and it is now "current". If portal row deletion is permitted for this portal, you can now select Delete Record from the records menu and this related record will be deleted instead of the current record of the layout where this portal is located.
Only way to prevent this is to size all the fields and buttons so that there is no way to click inside the portal but outside a field and button. If all else fails, you might place an invisible "do nothing" button behind all your other objects in the portal and size it to completely fill the portal row.
thanks I will try a "do nothing" button. I ask because I am using this with the iPad.