Are you sending any data out or just getting hits on ports?

When you connect to the network, then disconnect later, two things may happen that cause people to send data to your machine on port 6436.

1) You have been entered into hostcaches, and people are trying to use you as a connection point.

2) You have a file someone wanted, and their client keeps trying to connect even if you're gone. (This would probably happen a lot if you close down while someone is downloading)