Why do bluetooth speakers reconnect to device that is off?

I have several bluetooth speakers, and more than 2 iOS devices. Once a speaker is paired with one iOS device (iPhone, for ex.), the next time I turn on the speaker, it connects (with beep sound) to that device again, even if that device is OFF, preventing it from connecting to a different iOS device I'm trying to use it with (iPad, for example -also previously paired with the speaker). I'm wondering if the latest Bluetooth specification has eliminated this annoying trate.