[Drifty1]

I believe the systems on have fluid on both sides of the cylinder at the same time. So if you have no air in the system your fluid level should not change in the extended or retracted position. But there might be a internal relief that could be reliving before your slide is all the way to the end of the stroke. This could be caused by some restriction on that slide. But if it works fine when you close it with the other slides blocked at the manifold then it could be that every slide has a relief built into it at the manifold. They might do this so it prevents you from damaging a slide when you run them one at a time. Guess I might have to break out the manual to see how they are plumbed.