[talkSAFT]

Silver, This is the official FA regulation on Offside, but I can't see any mention on the point you raised about moving back onside and still being penalised:-

Offside offence
A player in an offside position at the moment the ball is played or touched by a team-mate is only penalised on becoming involved in active play by:

   interfering with play by playing or touching a ball passed or touched by a team-mate or
   interfering with an opponent by:
   preventing an opponent from playing or being able to play the ball by clearly obstructing the opponent’s line of vision or
   challenging an opponent for the ball or
   clearly attempting to play a ball which is close to him when this action impacts on an opponent or
   making an obvious action which clearly impacts on the ability of an opponent to play the ball

or

   gaining an advantage by playing the ball or interfering with an opponent when it has:
   rebounded or been deflected off the goalpost, crossbar or an opponent
   been deliberately saved by any opponent
   A player in an offside position receiving the ball from an opponent who deliberately plays the ball (except from a deliberate save by any opponent) is not considered to have gained an advantage.

A ‘save’ is when a player stops, or attempts to stop, a ball which is going into or very close to the goal with any part of the body except the hands/arms (unless the goalkeeper within the penalty area).

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On that bit about 'can't pick up after gathering a ball last played by himself', there's no mention of that in The FA Laws:-


".....a deliberate kick of the ball with your feet, or a throw-in, to your team goalkeeper. It results in an indirect free-kick to the opposing team if the goalie touched it with his hands or arms. Playing the ball with the knee, thigh, chest, or heading the ball, is within the rules of fair play."