jmtd → log → nautilus sums

I've got a ISO image that I wish to burn to DVD. I've got a copy burned already which has the same MD5 sum as the ISO file. I've just attempted to burn it another two times, both using nautilus cd burner (well, right click and 'burn image'). In both cases, the sum ended up being different, but strangely, the sum was the same for both of these subsequent burns.

Has anyone else experienced problems getting 1:1 burns with nautilus cd burner?