Any arrows (including survival player's and skeletons' arrows) hit blocks twice and create double sound. This bug exists since 13w36a, watch screenshots for details.
How to reproduce:
Shoot an arrow at a wall
Result:
You will hear double arrow hitting sound, sometimes arrow falls down and rarely returns back, but when it falls down and hits another block you hear second sound.
Duplicate of MC-29475 - If you have not, please use the search function in the future, to see if your bug has already been submitted. If you could not find the original report, please comment with the keywords you searched for.