The Import Roster function is changing the league_id value in college and HS* stat lines from 0 to the id of the top-level league (for our league, 100) for players imported. This results in those players having high school and college stats included with ML stats in some areas of the game (HTML at the least). More info
in this thread.
Our league file is here for reference:
http://www.thefobl.com/exports/FOBL.lg.tar.gz (though yes, this is in 15). I attempted to submit a ticket but received an error page after submitting the form.
* I believe this is not really related to those specific league levels, but any instance where the team_id is 0