Description of the Issue

In a Notepad++ document that is encoded as UTF-8 (no BOM), many Unicode characters are not displayed, but the hollow square appears in their place. If a displayable Unicode character is added to a line containing undisplayable Unicode characters, those undisplayable ones suddenly appear. Removing the "good" one makes the others revert to the hollow square. A simple example:

☆◬⊗⊠⋆⧆⨂

Paste that line into NP++ and you will see all the characters. Remove the leading star ☆ and the others become squares. Restore the star and the others re-appear.

Steps to Reproduce the Issue

1. Create a UTF-8 (no BOM) text file. (This is the only hard part of the procedure.)
2. copy & paste the following string into a UTF-8 (no BOM) Notepad++ document: ☆◬⊗⊠⋆⧆⨂
3. all of those characters will display properly
4. delete the leading star ☆
5. the other characters become hollow squares
6. restore the ☆ and the other characters reappear

Expected Behavior

All of the characters always should appear.

Actual Behavior

They only appear if an always-acceptable Unicode character is on the same line. If an always-acceptable Unicode character is in the document but not on the same line, certain Unicode characters, such as, but not limited to, the ones shown above, will not be displayed properly.

Debug Information

Notepad++ v7.5.1 (32-bit)
Build time : Aug 29 2017 - 02:35:41
Path : C:\Program Files (x86)\Notepad++\notepad++.exe
Admin mode : OFF
Local Conf mode : OFF
OS : Windows 10 (64-bit)
Plugins : ComparePlugin.dll mimeTools.dll NppConverter.dll NppExport.dll NppFTP.dll NppTextFX.dll PluginManager.dll SpellChecker.dll

This occurs with characters from many of the Unicode blocks.