Some top level items in Preferences dialog open an empty page. That page widget seems to be in wrong position and does weird things. See the attached video where the page is outside the dialog, on eeschema main window. It's stuck there if the dialog is closed when it's visible.
This is probably platform dependent, it doesn't happen with the latest nightly build on Windows.
Application: Eeschema
Version: (5.99.0-14-g548dbb7c2), release build
Libraries:
wxWidgets 3.0.4
Platform: Linux 4.15.0-58-generic x86_64, 64 bit, Little endian, wxGTK
Build Info:
wxWidgets: 3.0.4 (wchar_t,wx containers,compatible with 2.8) GTK+ 3.22
Boost: 1.65.1
OpenCASCADE Community Edition: 6.9.1
Compiler: GCC 7.4.0 with C++ ABI 1011
Build settings:
KICAD_SCRIPTING=ON
KICAD_SCRIPTING_MODULES=ON
KICAD_SCRIPTING_PYTHON3=ON
KICAD_SCRIPTING_WXPYTHON=ON
KICAD_SCRIPTING_WXPYTHON_PHOENIX=ON
KICAD_SCRIPTING_ACTION_MENU=ON
BUILD_GITHUB_PLUGIN=OFF
KICAD_USE_OCE=ON
KICAD_USE_OCC=OFF
KICAD_SPICE=OFF
Doesn't reproduce on Mac, but I'm pretty sure I know how to fix it....