Website incorrectly displays premium economy fare as first class

Airlines change their booking classes from time to time, and some changes mean a particular code refers to a different class of service than it used to.

Earlier this year Qantas changed booking class R from premium (A380) first class to premium economy class. Some online travel agent websites failed to note the change. What happens if you book expecting first class (at a relative bargain fare) and only get premium economy class?  Follow the discussion in the thread.