It doesn't make sense. You are using the correct pushrod ? Correct length? With the rocker arm removed and using the rocker stud as a pivot point, make sure the valve spring compresses enough so that the valve is opening all the way. If the valve is bent or stuck and won't open, that will cause the rod to bend. Might also be an idea to change that lifter if you have another as that seems to be the only one giving you problems.
