Well I did a reset on the Radio portion at lunchtime and re-programmed in my presets again. Most automatically downloaded the logos within a few minutes, but interestingly neither "Gold" or "Absolute Radio 80s" did. I then popped in an SD card with my logo's on, and selected the correct logos for the missing two stations.
When I went into info view (the logo and the track text view), the both displayed a larger version of the preset logo (hurray I thought, sorted at last). However after about 5 minutes, the Absolute Radio 80s" larger icon re-populated itself with the "Gold" logo, and the "Gold" radio station info view - repopulated again with a blank image place holder (this is despite the preset logo's staying the same). I can only guess it must be something that comes in over the air that's over-riding the logo's I put in in the Info view ?