I've experienced this in the past when the system 'forgets' who the controller is. As far as I know, the 568 must be controller and rather than set the others to auto (thus letting them fight it out in the comms trail), I set all the others to non-controller specifically. I seem to remember Des telling me to also run the volume control all the way down to zero so that zero registered on each item. As noted above, pressing clear on the MSR is also designed to re-set the controls.
When my 596 went mad with 1.21 recently, it meant that both 596 and 568 were fighting for control. The first I saw of this was the very erratic volume behaviour as both units were picking up the IR.
Rgds
NickL

Rgds,
Nick