i'm no expert but it might be something like this:

it could be that 8 of the people had lousy conections but one person had a very good connection.

then the person with a good connection left and another with a bad joined.

it could also be that instead of leaving the one good person was not doing anything for a while so he connection was free to send but then he used it to download something huge of the net or limewire or whatever and that cloged up his connection.

hope that helps.

-Johannes