MUPs are just full of people who are going to do random things and cyclists need to slow down and be on the alert. And people at work think I am weird when I say I prefer the road with a 3 ft wide bike lane, not much traffic and 35 mph speed limit to the MUP. Joggers and other cyclists seem to know the rules of the MUP and do the right thing when they hear a bell or ON YOUR LEFT. When I am walking on the mup and someone behind me signals me I usually raise my hand to acknowlege that I hear them.
On the portion of my commute that I am on the MUP and I leave for work late, I meet up with a group of older people who go out for their 10 am walk. The always walk spread across the entire mup. When I yell ON YOUR LEFT, many of them stop and turn around and look. One woman told me to get a bell. But I still think if they heard the bell, they would still stop and turn around and look. Since ON YOUR LEFT seems to be lost on these folks I just yell COMING THROUGH and they seem to be happier with that.
I see a good number of people walking like they do on the auto roads: facing traffic. I've just learned to slow down and be prepared for anything. Bells are OK for joggers and other cyclists, who seem to know the rules of the MUP.