One further thought: My Meridian dealer tells me that such "ghost" problems (occasional missed commands) can be due to grounding problems. They suggest connecting every unit to the same outlet via plug strips. I have no evidence this works as I have set my system up that way and still have the problems once and a while. Mute seems to engage properly but does not release all units at once. My center channel (DSP5000C) stays muted till I hit the mute button a few times.
KDM