Are seeding torrents actively uploaded?

[knapo]

Does Deluge Torrent actively try to upload seeding torrents? More specifically, does it fetch a peer list for torrents that it is seeding, pick some of the peers and contact them, offering to send some pieces?
Or, it only passively waits and listens if somebody else takes the initiative and connects, asking for pieces.

I'm asking because I see some (completed/seeding) torrents active (uploading), even though I'm behind a NAT and have both UPnP and NAT-PMP turned off in the settings. (I do not have this turned off normally, it's just a test I'm doing now, trying to undrestand some BitTorrent principles). Thanks very much.

[Cas]

If you have a listen port set and rule applied to firewall then UPnP or NAT-PMP are redundant, also you sometimes need to restart Deluge to ensure those extensions are not running.

[knapo]

If you have a listen port set and rule applied to firewall then UPnP or NAT-PMP are redundant

I'm behind a NAT, with no port-forwarding configured on it, so I would say UPnP or NAT-PMP are essential in order to be able to accept incoming connections.

And I'm also interested in the seeding strategy - is it possible that Deluge would actively seek peers to upload the (seeding) torrent to?