pipe delay time not stable

So when I use pipe in a M4L patch, when I first open Live, timing is correct, but after editing a device , at some point pipe's delay time will go wrong, sometimes shorter , sometimes longer, but consistently so. I have to reload a song to get the timing back to normal. Also, if I mute and unmute another default m4L MIDI device, on any track, the delay time of pipe varies significantly and differently each time I unmute the device, horrible!
This seems like a bug ? Its hard to reproduce, because it starts occurring as far as I can tell, randomly after editing a device, but here is an example