Software Update "automatically download NEW updates" option

I have been attempting to set up the Software Update service on my server to run in manual mode (allowing me to approve updates before they are pushed out to my client systems, and to conserve download bandwidth), but to also automatically download new updates (and ONLY new updates) to the server as they become available. However, every time I put a check in the "automatically download new updates" checkbox, the service immediately changes every "Available" update in the list (going all the way back to the oldest updates from eight years ago) to "Waiting" mode and begins downloading them ALL (or at least it appears that's what it is doing). Is this option supposed to only download NEW updates, as I was hoping, or am I right that it actually regards every update that hasn't already been downloaded as a "new" one that needs to be downloaded (which makes the option virtually worthless to me)?

I only have a 2 TB server, and have neither the space, nor the bandwidth, nor the desire to download tens of terabytes worth of unneeded old updates. Does this mean that I have no choice but to leave that "automatically download new updates" option unselected and manually select every new update for downloading as I see it become available (which is sort of a pain, to say the least)?

Any clarifications would be most appreciated. Thanks!