I just received a soulbound-on-aquire item as a reward for exploring one of the borderlands maps. I thought the random items we received were not supposed to be soulbound. At least, the overwhelming majority of items I’ve gotten have not been soulbound-on-aquire. The item in question was a “Strong Ring” and the map was one of the borderlands maps (I’m not sure whether it was the red or blue one, though).