I have read what IMGBURN Author respond to Obvious on Feb 2010 about the file burning order, I checked the option as you instructed to keep the Source Order but may be this apply if you are going to burn the files directly to a cd/dvd, actually I have not tried this, but if you build a ISO image in Advanced mode the file/folder order will be sorted in alphabetical order anyway, NOT in the order you added in the list. I tried this many times I checked the iso file with ISOBUSTER and always the lba order be enforced according to the alpha sort of the files
Some suggestion ???