Tried in Item Filter Editor->Vendor Filter->Add Filter->put "Portal Scroll" in name and type, select "match any" check box->select Currency in rarities. It does not work.
Vendor filter will be overridden ALWAYS by the save filter. If you have portal scrolls being 'saved' then they will not be sold no matter when vendor filter you have.
So have a look at your save filter, currencies fitler. It will save everything, so you need to add an exception in there, item name:
Portal Scroll http://i.imgur.com/2jhiWP9.png