I cannot confirm if this is a bug, but based on the official wiki it is. The wiki says that a villager can detect it's work station from 8 blocks horizontally or 9 blocks below it. It mentions nothing about 9 blocks above. I was able to on multiple attempts with a workstation up to 9 blocks above the villager have it take the profession of the block I placed. Once I reached 10 blocks, it would no longer accept the job or profession of the block I placed.