When you throw an item into the lowest level of lava from 1 block away and place a hopper underneath the lava and hoppers next to the lava, the item lands in the hopper but will play the burning sound and will bounce. It does not matter what Y coordinate you're at. This will sometimes work in survival or on the not-lowest block of lava. This will only sometimes work. I have tested this in 1.6.4 and the bug was there. This usually happens when you're facing west, but it also happens when you're facing other directions.