ImgBurn doesn't make the break if it can't find a good sector -- it gives you a message proclaiming the "end of the world" instead.
This is to do with the rendering software you use not understanding the dual layer format very well. You need better production software. Your long MPEG2 should be rendered in a way that your burning software can appreciate, then it will make the break no problem. It's a limited range of sectors that can be used.
I had the problem with Cyberlink Power Producer. It rendered nice long movies but not in a form that ImgBurn could use. You need a better production suite.