I just tried booking SFO to JNB, with an overnight in AMS on the outbound, and a stopover at CDG on the return.
It shows me the correct price (about $1,300) until the last screen before payment, where it then tells me there is no more availability in economy and I have to pay $10,000+ for Business class instead.
Tried it again and got the same behavior.
Went to Airfrance.us and was able to book and pay for the same itinerary at the proper $1,300 price.