Closing Symbol Editor that was opened from KiCad window generates duplicate/ghost child project in project tree

Description

See gif. Opening and close schematic symbol editor in a dummy project is creating a "ghost" test.pro child item to the test.pro project. Double clicking that ghost item makes it disappear.

Steps to reproduce

1. Open KiCad project in KiCad window
2. Open Symbol Editor
3. Close Symbol Editor

KiCad Version

Application: KiCad
Version: (5.99.0-1673-g84160c1da), release build
Libraries:
    wxWidgets 3.0.4
    libcurl/7.66.0 OpenSSL/1.1.1d (Schannel) zlib/1.2.11 brotli/1.0.7 libidn2/2.2.0 libpsl/0.21.0 (+libidn2/2.1.1) nghttp2/1.39.2
Platform: Windows 8 (build 9200), 64-bit edition, 64 bit, Little endian, wxMSW
Build Info:
    Build date: May 14 2020 23:54:07
    wxWidgets: 3.0.4 (wchar_t,wx containers,compatible with 2.8)
    Boost: 1.71.0
    OpenCASCADE Community Edition: 6.9.1
    Curl: 7.66.0
    Compiler: GCC 9.2.0 with C++ ABI 1013
![ua3jxtnmV2](/uploads/bc485e6f60eb4e6ad96c3f140a4009cd/ua3jxtnmV2.gif)
Build settings:
    KICAD_SCRIPTING=ON
    KICAD_SCRIPTING_MODULES=ON
    KICAD_SCRIPTING_PYTHON3=OFF
    KICAD_SCRIPTING_WXPYTHON=ON
    KICAD_SCRIPTING_WXPYTHON_PHOENIX=OFF
    KICAD_SCRIPTING_ACTION_MENU=ON
    BUILD_GITHUB_PLUGIN=ON
    KICAD_USE_OCE=ON
    KICAD_USE_OCC=OFF
    KICAD_SPICE=ON