This is how mine works: I use AFS and have focus on the back button AF/MF and focus magnify on C1 (focus is disabled on shutter). If i AF and then press the magnify, I get the "not available" message. If I AF and then move the MF wheel, then I can press C1 and get the magnify. I can press the shutter and continue to magnify for the next shot, as long as I don't press AF. If I use AF to get close, then I need to touch that MF wheel before magnifying.
Yes thanks Cindy, I just figured that out too. I need to touch the wheel a little bit then I can magnify it. Quite a strange implementation but it works.