NOTE: My sincere apology to the person who asked this question: I forgot to post it. The best part is that it is relted to the one I anssered this morning, q.v.
Team A wins a corner on the bench side. I’m positioned at the intersection of near side penalty arc and penalty area (solo ref).

Team A player goes to retrieve the ball. While Team A player retrieves the ball, his teammate exits the field from the near side goal line, jogs around the goal, then re-enters the field from the far side goal-line. I made eye contact with the attacker and let him back on play. Team A then took the corner kick and play resumed as normal.

It seemed as if the attacker did not want to go through the congested goal area. Could this be considered “trickery”?

Should I have cautioned the attacker for leaving the field without permission? And if I was going for a State 5/6 level, would this be an automatic fail in itself?

Answer (September 3, 2013):
A good question and one answered within the Laws themselves. This answer will be considered “wrong” by many purists, but it is founded in fact. What you describe is surely an unusual play, and the correctness of the decision to allow play to restart hinges entirely on the matter of congestion and the referee’s interpretation of the word “accidental.” If the area was indeed so congested as to present a barrier to the player’s becoming involved in the upcoming play, then what he did was fine — and no assessor can say otherwise. See “Interpretation of the Laws of the Game and Guidelines for Referees” (in the back of the Law book):
If a player accidentally crosses one of the boundary lines of the field of play, he is not deemed to have committed an infringement. Going off the field of play may be considered to be part of a playing movement .

This matter was also covered to some extent in the old Advice to Referees on the Laws of the Game (2012/2013), though this concerns the ball being in play, rather than a stoppage in play:
Players are normally expected to remain on the field while the ball is in play, leaving only to retrieve a ball or when ordered off by the referee. If a player accidentally passes over one of the boundary lines of the field of play or if a player in possession of or contesting for the ball passes over the touch line or the goal line without the ball to beat an opponent, he or she is not considered to have left the field of play without the permission of the referee. This player does not need the referee’s permission to return to the field.