waiting to retry - problem

I set 10 threads and connect to server that has enabled only 1 thread transfer. 1 thread downloads (thats ok), two other threads sets to status: waiting to retry (thats ok), but after the first thread is finished, that two other threads with status "waiting to retry" do nothing for about 10 seconds ... afterwards one thread starts download (or I have use stop and start buttons). (I'm using global queue)

thx for advice