One question as I haven't owned one of these models. Shouldn't the lever stay right of center when the gun is open?
I too have never owned one of these, so not really sure. I have seen single bolt guns on which the bbl lug below the locking notch was so shaped as to cam the bolt back & then let it snap in upon closing. Whether this gun was so built, I don't know or if he just tripped the catch or it is perhaps malfunctioning.
Many double underbolts use the front lug surface as a bolt cam, thus doing away with the catch & allowing the lever to return to center when open.