You would merge the playheads. So each play object would create a dim playhead, and they would move as they do, then when both are on the same spot the playhead would get brighter (to show both being present), then only one stream is sent to the actual device.
From what you’re describing it was sending two completely different messages which would behave as you described, when one moved off, it would turn itself off, taking the other step with it.