EESchema - Plot-directory "forgotten" after closing an re-opening EESchema

Choosing a custom directory under File->Plot and adding (relative) path works, but setting is lost if EESchema is closed and re-opened. Compared to *.pro-file the entry "PlotDirectoryName" is not present in *.kicad_pro-file

Version:

Application: KiCad
Version: (5.99.0-2195-g476558ece), 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: Jul  6 2020 09:07:55
	wxWidgets: 3.0.4 (wchar_t,wx containers,compatible with 2.8)
	Boost: 1.71.0
	OCE: 6.9.1
	Curl: 7.66.0
	Compiler: GCC 9.2.0 with C++ ABI 1013

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_SPICE=ON