We did upgrade from version 6 to 6.1, and in doing so transferred all the dll files accross into the bin folder as well as replacing the Cute_Soft_Client folder. I also did this when I reinstalled the control.
I have placed the editor in a blank project and all the buttons are fine in this project. So obviously it is something in our application which is affecting the toolbar image assignment process.
Interestingly, upon doing a quick comparison with FireBug between the correct one in the blank application and the one sat in our app, the themeindex attributes for the images display a discrepancy. For the images which are correct in both, the themeindex has the same number. However, for all the images which are incorrect, this themeindex does not match between the two editor instances.
I will investigate further down this route and post anything which I may find.
Many thanks,
David.