Bow replacement during attack animation removes attached arrow
When a bound weapon or armor normally expires, it switches back to the original item that was equipped before the effect was applied. This applies even when "charging up" a weapon, or in this instance, drawing an arrow and aiming. Should the effect expire, and the previous weapon was a bow, the arrow will still be drawn, but the arrow is effectively gone until you fire, whereupon the arrow fires normally. It is normally impossible to "dry fire" a bow without arrows.