With kernel 2.6.12.1 onDebian.
Setting the number of slots allocation to 3 instead of two, as set up at install time, allowed at least 20 upload connections! The uploads speed, which I set at 54 Kb, was up to over 100 Kb. Bringing the number of slot allocation to 2 , brought the number of upload to 2. And I can reproduce the problem. If you need any output from my box pls ask.
Thierry