Has anyone had this problem? I get the parallax set @ 50 yds. and then shoot and it needs to be set, just a little, to be set again. Reset it, shoot, adjust again. Do I send it in or ia there an adjustment that I can make to keep it set. Can't tell if the knob is moving because it only takes a very little move to get it reset. Has only been used about 100 times and 90 of that was trying to get it set.