In the center position, hydraulic flow does not go to the remotes. Moving a lever one direction directs flow (proportionally) to one of the quick couplers (of a set) with return flow coming back through the other coupler. The other lever works similarly via the other set of couplers. The quick couplers are designed to prevent any flow when disconnected.
At least one lever probably has detents to hold it in the full up and full down position. These detents are useful for attachments, like backhoes, which require a continuous hydraulic flow. But the detents can also cause a "deadhead" situation if accidentally engaged, which is surprisingly easy to do by accident. Except for the detents, the levers are spring-loaded to return to neutral, center position.
