This is commonly an issue if you use intelligent managed network switches, and is not a fault in ZXTM. Some of the more advanced switches can take a little time (anything up to a minute, in some cases), to activate the network connection of any machine newly plugged into the switch. This delay is caused when the switch sends out spanning-tree network discovery packets - it is trying to determine if you have plugged a new network switch in, rather than just a single machine.
These network discovery tests can generally be safely disabled on the switch. Please check your switch documentation to determine 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
