It seems as though the tuner only mutes the output, not the loops. This causes issues in two scenarios: 1. When the preset is on a swell preset with a long sustain, the output is muted during tuning but unmuting can cause the remnants of the swell preset to ring out. Happened to my friend who borrowed my board this morning! 2. When one of the loops goes to an external output (like a line mixer). If the external output just goes to the amp (without returning to the PBC) the tuner does not mute it.