I'm going to throw a kink into this discussion. I have two old Canon A2E (AKA EOS 5) cameras and the Canon 1.4x and 2x extenders. With some of the Canon lenses, the exposure compensation with the extenders is not the standard stop/2 stop.

There's a compensation table for the extenders when used with certain lenses on the A2E bodies. I've also used them on a Rebel body and there is no compensation necessary. It's an odd little glitch that would mean nothing to you unless you're using A2E/EOS 5 cameras.