InstaDMG Output and SIU

Hi, Is it possible to use the instaDMG output 10.6.7 vanilla dmg as the defined image source in SIU. When I do use it in a SIU workflow by mounting the dmg and defining that as the source, I find that it ignores subsequent actions such as "Add User Account" or "Apply System Configurations" and just spits out the same image that I started with. SIU logs that the image process was OK but it isn't. By using the instaDMG vanilla latest dmg it obviously saves adding subsequent packages to the "original" Mac OS X installer dmg. These actions do work when I use the "original" Mac OS X installer dmg. - Using SIU 2 10.6.7. Am i doing something wrong??