When an arrow gets shot into a block, it resettles itself once before coming to rest, causing the arrow impact sound to play twice in quick succession.
You can test this by firing an arrow into most blocks.
Linked issues
is duplicated by 7
MC-29641
Arrows make their collision sound twice in rapid succesion when hitting blocks
Resolved
MC-30857
Skeletons shoot once, however sound effect played twice
Resolved
MC-31003
Arrow's sound played two times
Resolved
MC-31940
arrows make the ''hit block sound 2 times''
Resolved
MC-32366
Arrow bug
Resolved
2 more links
Comments 24
14 more comments
Seems to be more than just the sound, the arrows precision itself is messed up. Possibly the client running the collision code on the arrow before the server does and the server adjusts? The difference can be seen from 1.6.4 by firing low power arrows into a block in front of you. In 1.6 the arrow hits and stays, while in 1.7+ the arrows usually fall off, stick to the ground, get stuck in the block, turn black, etc.
Confirmed