Fencer:

On this site they explain why:

8. A man or king may not jump over the same opposing man or king more than once.

9. Captured checkers are not removed from the board until all jumps made on the move are completed, and the hand is removed from the capturing man or king.

(It is only in rare instances that rules 8 or 9 affect the play of a game. They can have the effect of reducing the number of captures possible on a move. In most of these cases a king is the capturing piece. On very rare occasions these rules, either separately or in combination, will result in a king being forced to terminate a series of jumps on a square from which it will then be captured by an opposing man or king which itself would have been captured were it not for these rules.)

http://ourworld.compuserve.com/homepages/Arthur_H_Olsen/intlckrs.htm