I would say the birdhouses make the most profit per time in game, as its around 225 nests (75-80 hunter) which is around 700k+ plus the seeds in them, for maybe 5 minutes of game time an hour. But, we've spoke, you know my opinion :P.
I have also had this occurrence, was just glad I didn't find out the hard way on the HC, I usually watch now, and since ghosts ahoy isn't on stealth quester, ive been to lazy to manually unlock mort l0l. But definitely a problem.
All requirements are posted under the requirements section on the first page :). (5 hunter, bone voyage quest, fossil island unlocked)