The 5-20 and I believe all HD models have a different factory stop inside the turret. Apparently the added force applied when using the stops can damage the mechanism. Everything we tested in person did not show this to be the case, and I'm not sure how much force was applied to SWFA's test scope. Either way the verdict came from them, and we are left to make it right for the few sets that were sold.
We didn't see this coming and are sorry for any inconvenience to those that purchased the affected stops. Tim has emailed everyone in our records that purchased these stops.