I have two Ones stereo paired with a sub mini (room 1) and two stereo paired roams (room 2), all of them grouped in my living room. All working seamless for music listening.
Few days ago, I took the roams out to garden (they still hooked to the same wifi AP). Previoulsy I unticked the ones from the group so only roams would delivery music on the backyard area. Couple of minutes later my wife showed up at the garden saying I was driving her crazy with the deep bass inside the house, so I walked back in to realize the sub mini was playing along the roams!
That happened only that time, couldnt repeat it again. After tick and untick the (room 1) one time all when back to normal.