Is it a multi-session CD? I've had problems with those before, /could/ create the situation you described, but I dunno. There's definitely nothing wrong with using ISO-9660.
If it were problem "b", then I think you'd have problems reading the CD at all in the first place, but since it does mount, I don't think so.
So it must be "a". Something about the CD is non-standard. I'd fault the Photographer here, because I burn CDs on Windows often enough and have no problems reading them on my Macs.