Steps to Reproduce the Issue (STR)

1. Start with "new 1" as the only N++ tab (from a fresh install or portable version unzip)
2. Show the Document List Panel by ticking the box in Preferences > General; observe new docked window titled Doc Switcher appears
3. Create new tab with Ctrl+n; now have "new 2" in addition to "new 1"; observe Doc Switcher window looks like this:
   
4. Right-click "new 2" tab and choose Move to Other View from the menu that appears
5. Close "new 2" via the x on its tab

Expected Behavior

I expect the Doc Switcher window to only contain the "new 1" file because "new 2" is closed and forgotten about.
"new 2" should be removed from Doc Switcher.

Actual Behavior

Doc Switcher window contains both "new 1" and (the now-closed) "new 2":

Debug Information

Notepad++ v7.8.9 (32-bit)
Build time : Jul 15 2020 - 20:26:50
Path : C:\.................\npp.7.8.9.bin\notepad++.exe
Admin mode : OFF
Local Conf mode : ON
OS Name : Windows 10 Enterprise (64-bit)
OS Version : 1809
OS Build : 17763.1339
Current ANSI codepage : 1252
Plugins : mimeTools.dll NppConverter.dll NppExport.dll PythonScript.dll

Additional

This bug discovered when evaluating PR 8721 ; see here: #8721 (review)