Had the exact situation happen to me 2 years ago. Booked on Delta with Skyteam partner AF. Denied boarding on-ward from CDG to TXL. I got on the next flight but was treated very rudely by AF staff. As they insisted I pay a change fee. I refused as I has a non-restricted tkt with Delta. After some "checking" they were not too happy about admitting defeat!

Being Canadian I speak French and understood all that was said in french about how they dislike cheap American passengers. I responded in french that I was NOT American but I would forward their warm French hospitality back to all my American friends...

By the way the last few times I have flown into CDG is it me or there is always some sort of labour problem either with AF, airport staff, postal workers the country always seems to be on strike!