are you registering the images before integrating them?
by default, DBE only generates the background model. this is i guess so that you can evaluate it. if you want to make DBE do something, you have to set the mode (subtraction or division). again by default DBE generates a new image with the background subtracted, but if you tick "replace target image" it will do just that.
note that 99% of the time you should be using "subtraction" as the DBE/ABE mode.
rob