The bug
Anvils can be placed at a position certain blocks are already in, replacing them without dropping any item (exceptions: MC-40380).
See: http://youtu.be/8jv2ghTqxRE (ignore the item frame and painting part).
Affected blocks
Basically everything whose material is Material.CIRCUITS, see also orld.mayPlace(Block, BlockPos, boolean, EnumFacing, Entity) (MCP 9.40 names).
buttons
end_rod
flower_pot
ladder
lever
rails
redstone repeaters
redstone comparators
redstone_wire
skull
torch
tripwire
Linked issues
is duplicated by 33
MC-120102
Place an anvil where a lever is and you can overrite it!
Resolved
MC-133654
Anvil can be placed in same block as button
Resolved
MC-5668
Anvils will delete transparent items
Resolved
MC-6527
Falling anvil destroying some items but not others
Resolved
MC-6641
Anvil bug
Resolved
relates to 3
Comments 29
They did make it so that when falling anvils lands on any of those minor objects (torches, buttons, levers), it crushes and destroys them. I guess placing them on that block is similar to an anvil landing on that block, and you're just crushing that object by placing it there.
This might be working as intended.
Confirmed for 1.10.1 for stone button, lever, torch, redstone dust, normal rail, end rod, tripwire hook, ladder and flower pot. Others are untested. But there certainly is no new general solution in this version.
Nothing happening here when placing the anvil.