no success with RunEx too

I can also say it's not a problem with sharing the same graphical DLL
because I've also tested that using "setup.exe -s" to run in silent mode (no graphical interface)
same problem

I can't test it with another program as I don't know any other program that create a new process and exit (notepad or any common windows application don't fork).
I know only installshields application which do that.