I was once downgraded by BA from F to J due to an equipment change on a flight booked with hotel with BA Holidays. The original flights were booked during a sale, so were discounted. When I rang BA Holidays to ask about the refund due for the downgrade, their initial response was that as the replacement downgraded J seats were now more expensive to BA Holidays than the original seats booked, no refund was due (and indeed I should consider myself lucky that I was getting a more expensive seat!!). The flight was a BA flight too.
After a couple of calls this was dealt with properly and the the eventual compensation offer exceeded my expectations.
EC261/2004 downgrade 75% refund issues have to be clarified with the operating airline -> not the tour operator.