The custom shape primitive dialog shows the center as start point. The file format calls these start and end (but start is the center strangely. Might be something for v6 to fix as the file format is not really readable this way.)
My kicad version:
Application: ModEdit
Version: 5.1.4-1.fc30, release build
Libraries:
wxWidgets 3.0.4
libcurl/7.65.3 OpenSSL/1.1.1c-fips zlib/1.2.11 brotli/1.0.7 libidn2/2.2.0 libpsl/0.20.2 (+libidn2/2.0.5) libssh/0.9.0/openssl/zlib nghttp2/1.39.2
Platform: Linux 5.2.9-200.fc30.x86_64 x86_64, 64 bit, Little endian, wxGTK
Build Info:
wxWidgets: 3.0.4 (wchar_t,wx containers,compatible with 2.8) GTK+ 3.24
Boost: 1.69.0
OpenCASCADE Community Edition: 6.9.1
Curl: 7.65.3
Compiler: GCC 9.1.1 with C++ ABI 1013
Build settings:
USE_WX_GRAPHICS_CONTEXT=OFF
USE_WX_OVERLAY=ON
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=ON
KICAD_USE_OCE=ON
KICAD_USE_OCC=OFF
KICAD_SPICE=ON
@Rene, are you just requesting that the dialog "Start point" and "Centre" labels are swapped?