It has been very common that, when the GPS unit attempt to calculate the turn prompts, it misinterpret the route, hence giving false turn prompts. This is more challenging with City Navigator as it does not contain trails.
I have used various Edge mapping devices (705, 810, & 1000) with routes from various sources (GPSies, Ride with GPS, & Garmin Connect). While they work most of the time, there are enough times that they give me incorrect turn prompts. Instead, I rely on following the visible track on the screen.