Neighbor lost on interface flap

Hi guys, we use two machines running BIRD v. 1.3.8 as a bgp route-server on our IXP peering lan, and I noticed an apparently strange behavior: we had to reload the switch module on which our route server is connected, but after that, all v4 neighbors were showing "Error: neighbor lost", while all the v6 neighbors were ok. After quitting the daemon and re-starting it, all the v4 bgp peers were up & running. This happened all the times we had to reload the switch module, that is, all the times we "disconnected" the network interface from the peering lan. Any clue on what could be the cause of this? Thanks, Simone. -- This message has been scanned for viruses and dangerous content by MailScanner, and is believed to be clean.