I've noticed that improvised arrows (untested with other types) have a very long persistence timer.

Before logging out one night I shot around 15 arrows into a window at a fridge for practice.
When I logged in the next day (approx 16 hours later) all of the arrows were still there.
I've also noticed improvised arrows randomly around the map.

I imagine this will have a serious effect on server performance over time, especially with the recent rise in bow interest.

All the best,
Trevor.