I changed my preferences from "Keep enough work on disk to last between 0.1 and 2 days" to 0 and 0 days. My system immediately downloaded 18 WUs to a total of 25. I am trying to prevent it from downloading any more WUs as I must shut off the machine due to hot weather. This was easy to accomplish under S&H Classic and SetiDriver, but not under Boinic. You should add a function to turn of downloading of WUs, but not uploading. Also you should make preferences work correctly.

Set the allowed HD to say .01 GB. This ought to stop all downloads. Using 0 to 0 turns off the queue, but not the downloads for crunching. After the download that got the new 18 WU, it would notice that it had been changed, and the next download would be for a single WU.
jm7