Johnson joined the Heat (as apposed to the Celtics, who could've really used him in the playoffs), but his deal put them over the league's luxury tax line. In order to avoid paying the tax, Miami turned around and bought out Beno Udrih. Chances are the organization wouldn't have brought Johnson on board in the first place if it wasn't also able to dump Udrih's contract.
The thing is, there was no logical reason for Udrih to take the buyout. He was injured and out for the season, so another club wasn't going to sign him. What possible motivation might he have to give back money Miami owed him?
The Udrih buyout sparked anger and suspicion around the league as other franchises likely wondered if there was some sort of under-the-table deal between the Heat and Udrih:
"Hey Beno, you're not playing right now anyway, if you let us cut you and get under the tax line we promise to take care of you in the future."
Today, Udrih, who's been a free agent since February, re-signed with Miami, seemingly confirming the suspicions. League commissioner Adam Silver should void the deal and the Heat should be considered tax offenders for last season.