Folks, ... did it ever occur to anyone that when you move an IP address from the physical interface to the bridge as you should ... the MAC address of the physical interface is still in your desktop computer's ARP cache? And the bridge will of course have a different one? And you will not be able to reach the system for the "save" dialog until the ARP cache times out?
This is basic networking and 100% expected!
Increase the timeout for test --> save to 5 minutes.
Clear the ARP cache of your local system after clicking "test".
I'll bet a round of beer for all participants that this is the evil "cannot create bridge, TN is broken!!!" bug.