Running instaDMG deletes some local files

Hi all, I just want to ask if this happens to more ppl. I've noticed that everytime I run instaDMG it deletes Flip4wmv.app and Silverlight.plugin. This most probably is because MS pre/post-flight scripts and Im using the installers with no modification. It installs fine on the image but cleans in my host machine. Is this because of the unjailed installation in Lion? do you guys remove the scripts on these two packages? Regards, nbalonso