That is an issue on bike paths that are build inside a sidewalk, the cycling path is usually build using a smoother surface than the one designed for pedestrians. Plus it sometimes has a brighter paint.
I am pretty sure most people don't realize it but they are inconciously attracted to it. It just feels better walking on it.
No, every bike path in a city inevitably has crossings or is laid out next to a sidewalk. People just do their random-walk thing (Brownian motion, really, sometimes) and wander into the bike path.
That's an issue on any bike path in the US, even if it's a fire road in the middle of nowhere. I bet there are people walking their dogs or checking Instagram on the single track course that is used for the Red Bull Rampage.
Yeah, it happens on sidewalks, bike trails, mixed use trails, and dedicated bike lanes. If anything, dedicated bike lanes are the worst because they get errant pedestrians and cars.