There's a bug in the CM15A firmware which can make it do strange things. The bug surfaces when a CM15A has been disconnected from AC power without batteries for a long time, e.g., when you first purchase it. One (and probably not the only) strange thing is that the CM15A will not wait for a clear AC powerline before transmitting.
To clear the bug, unplug the CM15A from the AC socket and remove a battery. (The four batteries are in series, so removing one is as good as removing all.) Wait for a couple of seconds, then replace the battery and plug the CM15A back into the AC socket again.