Windows 7 startup items started twice

Problem:

In Windows 7 all my programs listed under the startup folder were started twice. If I removed them from the startup folder they were not started at all. In msconfig they were listed dubbel.
When I unchecked one of the dubbels the other (still checked entry) was gone on the next startup and the program was not started anymore.
When I checked the remaining entry again, the duplicate was back at the next startup and the program was started twice.
So I had the choice between starting the programs twice or not auto start them at all. Pretty annoying.

Solution:

I found the solution in the registry under the following key:

HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion\Explorer\User
Shell Folders\Common Startup

This key had my startup folder as value. Apparently the folder that is listed here is the startup folder for all user accounts ('common startup' :-)) which resulted in my folder items being started twice or not at all.
I changed the value to: C:\ProgramData\Microsoft\Windows\Start Menu\Programs\Startup
as it should be.