My best example is from last year, when I booked flights ARN-EWR-CUN-EWR-ARN using my AF/KLM FB miles, but on services operated by Continental.
When pricing this ticket as a revenue ticket on continental.com, the total taxes, surcharges, and fees came out to $85. I then simulated the same booking looking at a CO OnePass ticket and it was the same.
However, AF/KLM managed to charge me €335 while not a single flight was on their metal. I complained of course, and got a very silly answer back. While this a large sum, I would have been ok with this had it been on their metal. However, to charge this for a ticket on flights not operated by themselves is madness.
By the way, LH will do the same on a ticket on SK metal.