Here's a site I just now found addressing the ping-pong issue:
contraversial tackle law - The Rugby Referees' Forum
Note that it starts with a quote similar to what I and others have suggested:
Quote:
The IRB council meets in Dublin, where the Rugby Football Union, among others, will raise the issue of clarifying the tackle law which was passed at the council meeting in July. This states that the tackler is allowed to play the ball from any direction if he is on his feet, increasing the risk of the attacking team losing possession in dangerous areas.