I've noticed a few of my receipts post 3/3 have a section called "Add Collect."
The ticket shows the fare break down and total, then the ticket total, and tax separately again, then the fare rules etc. But below the fare rules there is a new section that says:
Add Collect:
An additional amount for the difference in fare was charged to VISA VIXXXXXXXXXXXX#### on Monday, March 5, 2012. $634.61 USD per ticket for an additional total of $634.61 USD was collected.
My employer questioned it as a "buy up" which is not allowed, however the full and total cost of the ticket was $634.61 after tax.