There is some messup in how WIN7 associates file names to a particular executable where it reverts back to the first instance installed. This small stub solves the problem in that it can be named as anything you like and placed in the directory where you want QE to run with a different file extension.
You rename it to a unique name, place it in the dir where you want to run QE with a different file extension then associate the file extension to this renamed stub. The OS passes the command line to the stub which in turn passes it to the copy of QE in the same directory.