This is an artefact of the sensors (radar) used. Since resolution and processing is insufficent right now, everything that is stationary is ignored.

I have a recent BMW with ACC that shows the same behaviour.

It's not an ultra rare event (I experience it roughly once every other day) and it's also not a problem as a driver.

Also with ACC: Just swerve right and ACC will happily crash you into any other stationary object like a lamp post or a wall.