Can NOT find new peers after a network disconnection/connection

[sa]

How to reproduce the problem.

1.Add 2 torrents(torrent A and .

2.Start A.

3.Pause A after it found peers.

4.Disconnect the network.

5.Connect the network.

6.Start A and B.

A will keep downloading,but B never start downloading because it can't get any peer.

Proxy is enabled.

DHT is off.

Ubuntu 11.04&10.10 64-bit

I guess that tracker does not work after step4&5.

Please help me.