When anvils are falling, they can break torches, redstone, comparators, repeaters without dropping them.
A complete list of affected blocks can be found at MC-1511.
Anvils replace some blocks when falling on them without dropping an item
Anvil doesn't destroy torches, redstone, buttons, etc. when dropped on them
Anvils won't drop as an item when falling on a torch/redstone torch.
Anvil can be placed in certain blocks
Blocks that fall and break on non-solid blocks will not fall when they are directly above a non-solid block.