Extremely slow upload if download speed is restricted

[Harkonnen]

I am trying to switch to using deluge on my server, but have problem with upload speed if i set ANY limit on download speed

Deluge 1.3.1, libtorrent 0.14.10, Debian Lenny, 100/100 broadband connection
Well, the connection cannot be used exclusively for torrenting , so i was aiming for 500K/500K limits, but as soon as set "max_download_speed" to any value other than "-1", my upload speed drops to 20-30K/s. Like without limiting download speed i get ~6M down, 500K up, set 500K download limit - speed immediately upon hitting "apply" drops to 500K down, 20K up...

Doesnt matter what exact download limit i set, doesnt matter what upload limit is set (could be "-1"), as soon as download limit actually restricts speed - upload drops to 20-30K/s

The only option in config that i think can affect this "rate_limit_ip_overhead" is set to "false"