Generally the way these work is that the hydraulic pressure is exerted on the cylinders in sequence. After one closes, the pressure is exerted on the next one until it closes, and so on. So your bedroom slide should close all the way so the pressure will build and close the next slide. With a leaky seal you may still be building enough pressure to close the next slide, but not enough to close the first slide completely.
Of course this is mostly conjecture on my part.
Howard and Peggy
"Don't Panic"