Description of the Issue

Notepad++ 7.7 will not insert exotic unicode / UTF-8 BOM correctly unless another, more common, unicode character is added on the same line.

Steps to Reproduce the Issue

1. Copy this line in Notepad++ as a UTF-8 text file:

⑨Till You Know

It will show as a block.
2. Add this character at the end of the same line:

～

Expected Behavior

⑨ Character should show up as long as document is in UTF-8 regardless of what's on the line. I've also noticed this behavior with the ♡ and ⑥ character.

Actual Behavior

When ⑨ or ♡ are inserted without another unicode character on the line, it shows up as garbage character ("□").

Debug Information

Notepad++ v7.7 (64-bit)
Build time : May 19 2019 - 13:05:35
Path : C:\Program Files\Notepad++\notepad++.exe
Admin mode : OFF
Local Conf mode : OFF
OS : Windows 7 (64-bit)
Plugins : DSpellCheck.dll mimeTools.dll NppConverter.dll PythonScript.dll

Comments

What's funny is that, despite showing up as "□", copy-pasting the character, you'll get the actual character when pasting...? I seriously don't know the scope of this; but it seems to be limited to very limited and exotic characters in the unicode space.

I dunno if it's related to this: ##5671

Here's a "GIF" of the issue:
https://gyazo.com/ba9402422dc6b32729b88c05bb9df161