The top 25 of every class in normal and hardcore are currently being checked every hour for changes (if unsynced in 12hr period) and the top 125 of every class in normal and hardcore are checked once a day for changes.
Also, the top 1000 players based on score have their positions on their character sheets resycned every day.
These checks, and in particular the hourly one, means that characters may move up and down the ladder on a regular basis.
The flag used in the "P3000" total experience ladder was previously incorrect for some players as some players were playing across multiple servers. This was changed to a "world" flag for a short while but has now changed back to a server flag, so an EU, US or Asia image is used again based on the server the player plays the most by way of checking which server has the most monster kills. This should hopefully reflect the correct region the player is from for the "total" experience section.