Avionics do not allow a total override of a weapon system as these articles claim. As someone who not only designs aircraft avionics, but also flew military aircraft, I can state this with certainty. It's a silly claim. It is purely propaganda and headline generation, nothing more.
If such technology existed, don't you think that it would have been used to prevent the numerous instances of friendly fire deaths that the US has experienced? Wikipedia has a nice list of such events (I'll start it at 1991 to keep it with recent history), and you'll see that many are aircraft related.
The one incident that really stands out in this list is:
In the 1994 Black Hawk shootdown incident, two U.S. Air Force F-15Cs involved with Operation Provide Comfort shot down two U.S. Army UH-60 Black Hawks over northern Iraq, killing 29 military and civilian personnel.
Another instance is:
US Patriot missile batteries fired two missiles on a US Navy F/A-18C Hornet 50 mi (80 km) from Karbala, Iraq. One missile hit the aircraft of pilot Lieutenant Nathan Dennis White of VFA-195, Carrier Air Wing Five, killing him. This was the result of the missile design flaw in identifying hostile aircraft
To further put this insane conspiracy to rest, keep in mind that whenever a nation buys sophisticated equipment, they perform operational tests on it. Any inherent flaws would be quickly discovered in a thorough test program. And many of the scientists, engineers, and military officers of these nations are taught and trained in the US, so they are not exactly what you would call incompetent.