longwinters........Its not uncommon at all......many shooters advocate a tap to set an adjustment thats been made, others myself included use the old benchrest technique of going a click past where you want to go and then coming back one. Either way this is only to settle the adjustment for the next shot.......when the gun recoils it does the same thing automatically. Its not something that would get out of whack or anything like that, its simply a way of making the adjustment movement settle to its desired spot when the erector tube cams rounded surface settles against the flat surface of the adjusters. It will seek its proper place with the jar of recoil or a tap or by going slightly past the point desired and then back. Not a big deal and most shooters do nothing at all and the next shot does the job for them.
Stringing usually points to bedding, pressure on a heating barrel, or over or under tightening of action screws. As GB mentioned its always good to center reticle and start with a full range of adjustment with a used scope. Some mounts offer horizontal adjustment and some like the Burris signatures offer both to help keep reticle centered for more precise adjustments. Scopes can also cause vertical stringing and would be a case where changing to another known scope and shooting would show if the scope was the culprit.
Hope you find your problem
woods
