Of course if a guy has cleared the test once, he ought to have done something right, and if he gets the clearance from the ICC, then the matter should be put to rest.
When an on-field umpire finds that same guy's action to be dubious again, he should be reported and made to go through the test again, but if he clears the test the second time too, then obviously it would mean two things, either the umpires are making the mistake or the tests aren't good enough.
Though my point is, if a bowler's action is considered bad, he shouldn't be labelled as a chucker, until it can be proven, because its never great for a bowler to have question raised against the legality of his bowling action, and that to when there is no evidence to back that claim.