issue here.

http://www.cbafaq.com/salarycap.htm#Q33
See section 33 regarding Bird Rights.

Kevin Love, Iman Shumpert, JR Smith, Thompson, and Irving were signed with Bird Rights. Korver was signed with Bird rights with another team and then traded to the Cavs, so his salary is allowed to go over the cap as well (I think ). Lebron was signed with "early Bird" rights which are some modification of this. Bird rights allow you to exceed the cap (and thereby pay a luxury tax). The problem is that if you trade for a player, their bird rights come with them:
"When a player is traded, his new team inherits his Bird rights. For example, if a player signs a three-year contract, plays two and a half seasons with that team, and is traded at the trade deadline in the third season, then his new team has full Bird rights following the third season."

I assume that is what allowed the Kevin Love deal with the Cavs. If this was restricted to drafted players that stayed with the team I think it would help with the issue.