Blocks such as repeaters, comparators, Redstone dust, Torch, Redstone Torch, Soul Torch, Lantern, Soul Lantern, Lever, Button(Any), Pressure Plate, Door(Any), Vine, Twisting&Weeping Vine, Ladder, Scaffolding, Flower pot, and Bell Can be placed at a candle with no problem whatsoever which is the same issue with lightning rods