Description of the Issue

Steps to Reproduce the Issue

1. Paste the following text into a blank document in Notepad++

☞
☞☛

Expected Behavior

In the first line, a WHITE RIGHT POINTING INDEX glyph is displayed, for the Unicode character U+261E
In the second line, the same glyph is displayed, followed by a BLACK RIGHT POINTING INDEX (U+261B)

Actual Behavior

In the first line, an empty square is rendered.
The second line is properly displayed. In fact, if a U+261B is appended to any sequence of U+261E, then all of them are rendered correctly; if the former is removed again, then the empty squares appear again.

Debug Information

Notepad++ v7.5.6 (32-bit)
Build time : Mar 19 2018 - 00:26:59
Path : C:\Program Files (x86)\Notepad++\notepad++.exe
Admin mode : OFF
Local Conf mode : OFF
OS : Windows 10 (64-bit)
Plugins : DSpellCheck.dll mimeTools.dll NppConverter.dll NppExport.dll

More info

Default font is Courier New
I guess this issue is not constrained to those characters, but it may be a symptom of a wider issue with higher-block Unicode characters.

Screenshot