Seems like you can't use emojis in usernames either, and using a single emoji as one's password is apparently a valid password (it converts it to the unicode the same way the username is)

This also breaks the URL field, which is technically a bug since emoji domains actually exist. https://en.m.wikipedia.org/wiki/Emoji_domain

(Punycode is an obvious workaround but it looks ugly.)

🦆

That's a good reminder about the passwords, because a future switch to UTF-8 would invalidate any password that contains off-page code points.

Emojis in forum posts was something I added a while back. Usernames never supported entity references other than & so I never included emojis in there.

If "the URL field" means BBCode or a member profile field, those are a little more complex than forum post text. Do you want to add that in the bug tracker for me?