Before I criticize I would like to compliment. I think Lightning UK ImgBurn is a great product. I even disabled Windows burning through a registry edit, and just use ImgBurn (and I think Windows now wastes less time looking at an inserted disc).
I have noticed with programs like ImgBurn that Canceling doesn't always work, particularly when a defect on a disk has arisen. It's likely that Windows restricts the ability of the program to implement a robust cancel button. That's why I requested to a disc manufacturer that the next version of Windows have "better optical media response." Defects happen and it should be physically possible for the software to tell the drive to just forget it and stop the spinning and allow ejection. If there is anything ImgBurn could do on its own with regard to a better Cancel button, or to communicating with the hard-headeds at Microsoft, I think it should do it.