uploading stops when downloading finishes

[wakeboarder801]

i'm having a problem uploading my torrents after it has finished downloading. the torrent will simultaneously upload/download fine (up to 2 MB/sec), but once the torrent is 100% downloaded, uploading stops. i can see that there are peers out there, and sometimes i'm even connected to them, but nothing will upload. i don't think there is a problem with my connection because i have tried uploading it at different locations (school and work) and it's the same problem.

hopefully someone can help me figure out the situation

Here's my info:

Insprion 9400

Vista Ultimate

uTorrent 1.8.2