when I connect a new AP (configured or not) all other AP´s will lost the connection to their clients. Sometimes it need some time before the network work again. In realy bad cases I have to restart the ASG´s.
The ssid´s are visible but the connection doesn´t work (the devices get no IP)
EDIT: also checked with Fluke AirCheck WLAN tester, so it is not a operating system problem