Given how the bed is effectively constructed as a channel group, it would have made sense to me to be able to solo or mute the entire bed akin to the standard grouped mute/solo behaviour. Unfortunately, the icon is greyed out and unselectable, even though it shows up; when I solo any one bed channel, only that channel is currently soloed.
The button you mentioned, and for which I put a picture below, is enabled only if the ADM file has groups. When this is the case, and more precisely if there is not a single group for all channels, then the button is enabled.
And when the button is activated, indeed, clicking on mute or solo will mute or solo all the channels of that group (from the track header or from the renderer UI).
In many ADM files, there is a separate group for the bed. In that case, you get what you want.
If you tell your clients to put a different group for the bed, it will work as you would like.
Now you could tell that if there is no group, WaveLab will consider a bed as a group and it will work in all cases. I agree with that and I might do that in the future.
I definitely expected for the bed to become a group even if it was not set up as one in the ADM file originally!