If say a 222 is connected to a 250DR, then the 222 is put into standby the 222 will mute (using relays) and the 250DR will stay on.
Soft-start
Not to be confused with muting
Soft-start limits the in-rush current on the mains when the large toroidal transformer is powered up. The soft start is then bypassed after 0.2 seconds.
This happens when the units are powered up from 0.5W standby mode.
The result is no light dimming, no RCD trips tripping, and kinder on mains fuses.