This has been happening to me since some time. It looks like it's not only me.
Some ranked maps that I have downloaded seem to ask me for an update, and even while they have ranked score
This happened to one of my maps (Miracle paint) and when I updated, one slider was missing.
I have not checked the other maps to see if something is missing, but It's still weird.
http://osu.ppy.sh/ss/18661http://osu.ppy.sh/ss/18662http://osu.ppy.sh/ss/18665(Tu peor error also asked me for an update, though it only asked for an update on the easy diff)
I think it has to do with the ranking date, as this maps have a similar ranking date. Those are the only pics I can post since I do not download all the ranked maps :<