After playing with SAC 4.0 some more, I'm pretty sure that 90% of the problems are related to running the three Mackie control surfaces.
As much as I would like to use Monitor mode (well, and 3-unit Mackie support), it's back to 3.1 for me. Can't afford to risk problems on a show where I'm being paid.
FWIW, I've also noticed the Mackies making random movements (especially when the system first comes up). I seem to recall people with Motormixes making the same sorts of complaints. My guess is that this is a generic bug in the control surface code.
The sad part is that it is pretty obvious that SAC blocks while waiting for the MIDI code to do its thing. For something like MIDI transmissions, it makes so much sense to fire off a separate thread for each controller and let that thread handle the slow data communications while the rest of the system updates the display, etc. Bob seems to be afraid of threads (I guess he doesn't realize you can set priorities so they don't execute during his time-critical mix engine code). I was under the impression that the display code operates in a separate thread already (and the MIDI code seems to be tied to that thread somehow as activating the MIDI code *really* slows down display operations). Too bad this can't be cleaned up. SAC v4.0 would *almost* make me really happy with SAC if it worked properly.
BTW, with the 3 mackie units attached, the load % on my machine goes from 33% to almost 60%. That seems kind of crazy given how little data (in the big scheme of things) gets transmitted over MIDI.
cheers,
Randy Hyde