...I have been looking in the wrong places:
I found if you innocently pop up the window from the Start menu Addons item "Addon Airports Configuration" there may be some added entries in either of your add-ons.cfg files which is causing the problems. I found some test code that gets activated by mistake otherwise IF would not add sections to those files.
The actual use of the auto-addons is working OK.
So unfortunately it does seem that IF has made some or all of those entries. I suggest you will have to repair those files by removing those bad sections if you did not have a backup of those files.
When the system is set up fully, make a copy of those add-ons.cfg files one in "C:\Users\you\AppData\Roaming\Lockheed Martin\Prepar3D v5" and one in "C:\ProgramData\Lockheed Martin\Prepar3D v5" before using the IF AA features again.
I will continue investigating in case of any more problems and get Preview 21 uploaded as soon as possible.
Apologies for this inconvenience.