Hey man, I see that nobody has answered. I'm not an expert but I suggest the following:
1. Your settings seem correct to me. If I wanted to make Deluge download only one torrent at a time, I would probably use the same numbers as the ones you have used in your screenshot, unless I already had a lot of other stuff going on. So uh ... what gives then?
2. Sometimes it takes a little while. Click the buttons down to number 1, and then give it two minutes (really! count to 120, "one-mississippi, two-mississippi, ..."). Any hanging data-requests (out-going and/or incoming) will want to complete themselves, or will at least want to send a signal to the other side that they won't be completing themselves, before they just abandon all hope.
3. Look at your "Bandwidth" settings, too. There are things in there (mostly self-explanatory, and/or well-explained in the documentation) that affect your total downloading and queuing situation. (Really? It's "queuing" not "queueing"? Spell-checker cramp!)
And ... the most likely solution? ... here it is ...
4. Try setting total active SEEDING to zero, since you allow yourself only ONE active torrent AT ALL. I think this may be your problem. If you are going to have one active download and one active seed, then you have two active torrents (as long as the download and the seed are not the same), right? So, change your "1,1,1" to "2,1,1" or to "1,1,0". Maybe.
Just a thought ...
