Go to the root Purchase Journal (NewViews > Journal > Purchase) and click the window pull down button and click trade information. Change your descriptions there. In a future release you will be able to change the description from trade information for that particular journal.
To have the correct journal appear in each entry that you make, press insert which will insert a new row and click on journal, type your PO-50% which show you a select journal table and press enter on the correct journal. Now right mouse click Edit > Default Value > Set (or key strokes ALT EVS or Ctrl KW). This will set the PO-50% to come up each time you press insert.
Press F9 on the entry in question (like NV1 GOX) is the entry you had mentioned the same entry you had entered?