Villagers will not walk or farm across water blocks with a lilypad on top of them if the only path is across them. They will lock onto a planted object they want to harvest from the other side, but will not walk across the block with the lilypad on it. They seem to be treating them as solid blocks. If a path exists to the object they want to harvest that isn't across a lilypad, they will route around the lilypads until they reach their destination. Unsure if this is only when harvesting food or if this applies to their general pathing around all environments.