I've noticed Gopher doing this on his playthroughs. He's set in firing position with his bow but then changes his mind and cancels the shot. I've never found out how to do this myself and have always been committed to firing once I've pulled the trigger. It'd be a big help if someone could tell be how to avoid taking a shot with my bow once I'm in firing position.

Use the button that you use to take out/put away your weapon - by default on PC this is R, not sure about consoles. It will return it to the unsheathed but arrow not yet nocked (?) position.

Hit the 'ready' key - defaults are R on the PC. X on XBOX and square on PS/3.

Ahh, so it's the unsheathe key/button I have to use! Thanks, you've been a big help! I'll have to try that next time I play (after I've finished the next chapter in my journal).