Shooting an arrow from a dispenser directly into another block causes that arrow to get stuck. It can't get picked up nor will it despawn. Sometimes it can be seen in an upright position and eventually returning to a horizontal position. The only way to pick it up is to destroy the encasing block.
In 1.6.4 the behavior is as expected; the arrow can be picked up and despawns.

Steps to reproduce:
1. Place a dispenser
2. Place a block in front of the opening
3. Shoot an arrow from the dispenser
4. Wait for the arrow to disappear or try to pick it up