Hughes "retro fit" lifter not pumping up!

I think I see what you mean.....if you are talking about the lifters that are on the heel of the lobe when the engine stops. Yes, the running oil pressure would 'bleed off' from the chamber at the bottom. But oil is an incompressible liquid, and the amount of volume 'bled off' to lower the pressure to 0 when not running is infinitesimally tiny, and the lifter is still 'pumped up'.

A lifter that is up on the toe of the lobe when the engine stops sees the open spring pressure pushing back through the pushrod. If the open spring pressure was 250 lbs for example, with a 1.5 rocker ratio, the pushrod is pushing down on the plunger with about 375 lbs of force. Just making a wild stab at the typical diameter of the plunger as being maybe 0.4" (I am in a motel and they won't give me a Mopar lifter to measure!), that would result in almost 3000 psi on that oil in the lifter's bottom chamber at rest....!!!

Yeah, I guess that the machining and check ball seal needs to be pretty good. That is making my head spin......