It's not just a problem for font authors. What happens with this can change the intent of what people are writing pretty radically. If someone tweets "I support [afghanistan flag]" and that's seen by the wrong people with the wrong font it can literally mean the difference between life and death for the poster.
See also, Mobile vendors change the gun emoji to a picture of a squirt gun. Are you sending someone a death threat or telling them to cool off with a super soaker?
Edit: Flag emojis aren't supported on HN