Pathways generated in biomes with trees are generated like bridges, going over other generated items like fences and houses. Lamps of all kinds are generated either on the same level of the path and in the middle (taking up a block space where it shouldn't) or taking up space on the actual path, or in the ground where it looks like it shouldn't. It's hard to fix yourself because it takes up so much time destroying the blocks then laying them down again.