os.startfile hanging onto the launched app, or my IDE?

[Josh English]

I have been using os.startfile(filepath) to launch files I've created in Python, mostly Excel spreadsheets, text files, or PDFs. 

When I run my script from my IDE, the file opens as I expect. But if I go back to my script and re-run it, the external program (either Excel, Notepad, or Acrobat Reader) closes all windows and restarts the program. This can, unfortunately, close other files I am working on and thus I lose all my changes to those files.

This is happening on Windows 7. 

I am not sure if it is Python (2.7.5) or my IDE (PyScripter 2.5.3).

It seems like Python or the IDE is keeping track of things created by the os.startfile call, but the docs imply this doesn't happen.

Is this a quirk of os.startfile? Is there a cleaner way to get Windows to open files without tying back to my program?

Thanks,

Josh