Randomly, I am unable to add more arrows to the stack of arrows in my inventory.  I can only fix this issue by quitting and saving and then going back into the game, whereupon I am able to add the arrows.

I have attached a short video of the issue as static screen shots would not show the issue.

To make it the video small enough to 'attach' it is of low quality and shortened, however I have put a higher quality and un-shortened version on YouTube at:  https://youtu.be/teK7XcHmrn4  I Hope this helps.