In the old days of paper boarding passes the European Commission (or some parts of it) required the original boarding passes when reimbursing travel costs. I guess some people tried to be clever, booked flexible tickets, used those receipts for the reimbursement claim, but canceled them and booked and used a cheap ticket instead. At least that was the only reason that came to my mind why they would request boarding passes in addition to the submitted ticket.

That said, I never had a problem with a higher cabin class on the boarding pass than on the ticket. This did happen a few times due to operational upgrades (economy overbooked) or due to cancellation of a booked flight. The boarding pass then typically showed booking class C or D, I think, but the original ticket had the economy booking class.