By chance I stumbled over a couple of highway=residential with an obvious wrong motor_vehicle=no a couple of days back, and did a quick query for that and similar likely wrong tagging (1'963 streets in total):
http://overpass-turbo.osm.ch/?q=LyoKVGhpcyBoYcSGYmVlbiBnxI1lcmF0ZWQgYnkgdGhl...
Naturally either the tagging could be wrong (should be likely destination or private) or the way classification could be off. Naturally there is always the chance that the street in question is actually correctly tagged so these need to be looked at on the ground (or at least with OSC or mapillary). I suspect some of these go back to times when the editor presets were not as good as they are today.
Simon