No, it is not a bug. You have same chance to get every possible item in that luck range where you are working. For example, I haven't find note, but I'm looking for about 2 months I believe. Not with Grave robber before update, not with any other job after the update. But I have about 5 jobs that has range 1 bit more then 1400. Still not lucky.
So it all depends on your LUCK to get certain item.