"They are causing a lot of bother and we are hoping that there will be a way to disable this "feature" soon"
Not gonna happen, devs said it's here to stay since it would break multiplayer to get rid of it. Coming to a full stop outside the 20 meter radius will unlock it though. AI trains are a different animal, even in TS2010 they lock the next switch ahead of them, and if going from double track to single and back to double they try to lock both switches before they enter the single track section;
http://www.trainsim.com/vbts/showthread.php?311523-AI-traffic-how-screwy-can-you-get
Properly signaled when 2 AI trains are fighting over who goes first it only takes a minute or so for them to play rock-paper-scissors so one of them goes, even improperly signaled they will sort it out in five minutes or less. When it comes to the player, AI considers him a low life bum who should stay out of the way of his betters, so whatever you do they will always insist on priority. I just work with that by checking the map, if there's an AI approaching that junction I'll stop and wait for him to pass before going myself, in other words yield right of way to all AI trains. Get caught in a Mexican standoff;
http://www.trainsim.com/vbts/showthread.php?306297-Beginners-guide-to-Trainz&p=1729753#post1729753
All that's needed is to order the AI to Stop Train, after a minute he will release the lock, then you can change back to your train and drive past, changing back to his to order him to continue schedule.
For really screwy situations where one AI is stopped blocking several junctions,
1. Right click in his F6 window, order him to Stop Train.
2. Click on his lead loco, hit the 1 key to jump in his cab, move reverser back and forth til you have control.
3. Drive him like he's a player train to someplace that he's out of the way.
4. Untangle the rest of the traffic jam.
5. Drive the AI to a place where he can get to his next trackmark (in other words don't leave him on a wrong way siding facing a track direction marker pointed against him or something) and order him to continue schedule.
You can also hijack any AI train by ordering him to Stop Train then Abandon Schedule, now it's a player train and you can stow it wherever you want.