If the internal piston in the replacement lifter was stuck higher than normally required in its new home. That is higher than the top extension in operation of a certain valves normal lifter. The valve would not totally close.. The distractor here is the lifter was not only a used one it was from a different location that required the usable normal internal lifter piston position to be much higher in the hydralic lifter than in the place it was installed in.

If it had been the original lifter with a stuck piston the valve would have closed and the worse senario if any would have been some lifter noise because of the additional valve lash resulting. Clear as mud? I find this difficult to describe. I feel it is probably accurate all the same.