i think it should be built into the next CBA that if a player is traded and then returns (30 days is fine by me) that he should be forced to take a MAJOR salary reduction by coming back to his traded team (I don't know what that percentage is, but make it sizable).
What this does is cause that player to think long and hard before returning to the team that traded him. It does not punish the rest of the teams who can pick him up (and I have no problem with that being the remaining of his pro-rated salary). The team that traded him now has to consider the repercussions of trading away a player they want back because he may not want to return at a lowered pay, when the other NBA teams can pick him up for his full salary.
I have no idea what the current rule is (regarding salaries of traded players who are re-claimed or picked up by another team) but the only way to change the current system is to PUNISH the team who trades him and punish the player ONLY if he chooses to return to that team... I can see no other way around this...