Usually means the subtotal stored in the database is no longer synced (it is not recalculated by Edit Orders). I've also seen this in the past when 'ot_subtotal' (Subtotal Order Total Module) is disabled (needs to be enabled for Edit Orders to work correctly). The most common cause is if there was an ERROR while updating an order (such as the `p` one you saw). Quickest fix is to just update the two related database tables by hand (if you really need to keep the order), or just delete and re-create the order.

For reference it will be the row in the table 'orders_total' corresponding to the row storing the value of 'ot_subtotal' for the order.