Didn't bother to read some of the above posts so don't know if this has already been said. In Yahoo Fantasy Football a Kick return is awarded to the individual player, not the D/ST. Touchdowns are only awarded to the defense from turnovers, whereas Special Teams TD's are awarded to the player.
For example when Percy Harvin ran that kick return or punt return, whatever, back for a TD, I thought my D/ST should have been awarded 6 points. Turns out the 6 points went to him as a player and thus all TD's resulting from Special teams, count as a players total points, not the D/ST.