I just noticed this phenomenon today. I had quite a short list of objects that I had muted (copybot, and that bloody awful banana phone!!) and no people at all. Today I discovered, by only being able to hear half-conversations at a gathering, that quite a few more objects and some people that I'd just met were in my mute list. I unmuted them and moved on.
Later on I went to a new place and stood around for awhile. Two people I have never met were obviously arguing but one of them was newly added to my mute list by the phantom muter bug. I could only see their half of the argument by clicking the Show Muted Text button.
I don't want to have this box ticked all the time on the off-chance that I run into that #@$* banana phone.
Known bug?
Chellonia Regent