The £4.80 ticket is the old Saver Half, i.e. a special web-only Off-Peak Single priced at half the price of an off-peak return. I seem to recall someone said in another thread recently that these have been renamed from Off-Peak Single to Off-Peak Day Single, so this seems to bear that out.
At a random guess, the reason for this was that Virgin didn't want people to have the month-long return validity, so they really are starting to sell two of these instead of an off-peak return, even though the price is the same (or 5p different with a railcard, due to rounding). Apologies for assuming the Virgin site had confused you! Bear in mind for the future though, that for the same price (or 5p more) you can buy a normal off-peak return that is valid for a return journey up to one month into the future. There isn't much point in buying two of these single tickets really.
I have to presume these tickets still have restriction code CS and are still valid on any train after 09:00 though, but I don't think it's possible to check from publicly available sources, since the saver half fares don't show up on National Rail Enquiries. Maybe someone with access to the Manual or Avantix Mobile can check for you.