In one of update logs it was stated that fuel manifolds now have an internal storage to feed engines more smoothly. This internal storage doesn't get saved when a vehicle unloads. To reproduce the issue, simply spawn any diesel-powered vehicle without keep-active blocks, and move away 3km to unload it, then come back to it. Some of the fuel (5-10 liters per manifold) will vanish. Saving the game ang reloading also causes this.