It seems that some bittorrent clients cache connections or sessions for a while and keep trying to connect.

It is possible that you are receiving fragmented IP packets. We recommend you modify this at the firewall: Security->Advanced->Advanced attack detection and protection->Miscellaneous section and modify
Do protocol analysis and Block Fragmented IP Datagrams options to stop such alerts temporarily.

Related Articles:
See forum article on Azureus
http://forums.comodo.com/index.php/topic,6058.0/topicseen.html