Has anyone successfully managed to control aux send via MIDI signals from the onscreen sliders on the MIDI mixer? (The manual gives a mini-tutorial on doing exactly this, so it's not entirely an esoteric question.)

I find that once I've tired to set this up as described in the manual, touching the slider causes the aux send to drop to zero, and that no amount of further twiddling makes it change again. Is this a known bug? Has anyone done this successfully?

Thanks in advance,