When a cylinder head is assembled with the correct spring, retainer and keeper the tip of the valve protrudes past the top of the retainer. If a plus retainer and/or keeper is used, the valve tip becomes recessed in the retainer. The rocker arm will contact the retainer prior to the roller contacting the valve. To make the roller contact the valve tip, clearance must be cut into the rocker and can cause the rocker to break prematurely.
In the past we have seen and heard of some customers raising the stand to clear the spring, unfortunately this sacrifices geometry for clearance and can now lead to guide wear issues. The best fix for this issue is to eliminate the plus retainer and/or keeper or add a lash cap.