This is commonly an issue with your network switches and not the balancer. Some of the more advanced switches can take a while (anything up to a minute, sometimes), to activate the network connection of a machine newly plugged into the switch. The delay is caused by the switch sending out spanning-tree network discovery packets - it will be trying to determine if you have plugged a new network switch in rather than just a single machine.
These network discovery tests can be safely disabled on the switch. Please check with your network switch documentation on how to turn these features off. For example, this web page documents how to speed up Cisco switches:
http://www.cisco.com/warp/public/473/12.html
