There was a bit of discussion here: http://cs.trains.com/mrr/f/744/t/182056.aspx and here http://cs.trains.com/mrr/f/744/t/189784.aspx
Since CV11 is not a requirement, some manufacturers use it slightly differently. The most known example is the default of CV11 in Digitrax sound decoders ends up having the sounds stop periodically on other than Digitrax systems. The way Digitrax command stations work, in a client-server model, any loco that is selected always gets a constant packet stream. Other systems will skip sending data to speed up the throttle polling, if no change was detected from the last poll. They send as often as required by the NMRA specs and no more. The idea of this use of CV11 is so that when you dispatch or release a loco, it will no longer get data, and the sounds will automatically shut off - no need to do a shutdown or mute when ‘parking’ the loco, but since the Digitrax command station keeps sending data even if you set the speed to 0, you can wait on a siding and the sounds keep going, but when you tie up and release the loco at the end of a run, it will go silent by itself.
–Randy