“What happened is some players would add the tuning to a legacy weapon, send to an alt, remove it on that alt, re-add it to the weapon, which would then incorrectly unlock it in collections on that toon,” the devs explained. “They would then send that weapon to all of their toons and perform the same process, thus circumventing the entire collection system and obtaining weapon tunings for their legacy without having to pay for it. As everyone has pointed out, crystals sold via the cartel market could also be collection unlocked this way, and in fact, as players have clearly stated in this thread, they’ve been doing that for a very long time.”
The exploit was fixed yesterday and can no longer be used in this fashion. However, with August’s Update 5.4, the team is including a change that will allow players to transfer crystals and tunings using legacy weapons at no cost.