I can't say i've experienced that issue.
Can you take a photo looking down the feedneck with the bolt in the back position?
All I can think... is possibly a square 114 oring - which is causing the bolt to move back a mm or so - if you pop out the drive train, can you see the square oring that acts as a bumper? When you put a ball in, does it roll about a lot? Is there a pillow bolt tip still in the bolt?
Just trying to think of a reason for it to roll back so far..