A wireless client will always connect to an SSID when the name (and keyphrase) are the same. There is no way to disable this behavior, but I can't think of a situation where you would want this anyway.
This way you can have multiple AP's with the same setting, connected to the same LAN in the back-end. This way a client can roam between access-points while walking over campus or in your building for instance and automatically reconnect to the strongest AP close to it and have little to no interruption to it's wireless signal and service.
(This is not interrupt-less wireless roaming some speak of, but often you only miss 1 ping or so and most applications won't even notice)
The key here is that the LAN in the back-end also needs to be the same. That way the client can keep it's IP (which it should get from a central DHCP server, not every AP desperately) and continue working.
Maybe explain better what you are trying to build and we can advise on how to configure that.