Tested, same results as yours.
Honestly I used the clavicles controller not that often, so I can’t tell if this is a new behaviour or not, but since ART hasn’t been updated in very long time, I think that what you’re experiencing has always supposed to behave like this.
In theory the clavicle controller should only affect the the angle, so is quite weird that you can literally shift the entire arm inside the body.
I guess that the developer added this ( and many other ) functionality to have the control rig to be as flexible as possible, considering that you can also do stretch and “non human” things.
Have you tried ART V2? is not Jeremy Ernst blog, but I still have to test it.