CPack: Segmentation fault when using FreeBSD generator

I'm attempting to use the CPack FreeBSD generator, but attempting to create a package results in a segmentation fault.

(The exact project I'm attempting to compile is SuperTux)

Full steps:

• Fresh FreeBSD install
• Install dependencies: pkg install -y pkgconf git sdl2 sdl2_image openal-soft glew boost-all curl libogg libvorbis freetype libraqm
• Install CMake from source:
  • portsnap fetch extract
  • cd /usr/ports/devel/cmake/
  • make configure
    • Make sure to check the "CPack" option in the first screen
  • make && make install
• cd ~
• Clone the project: git clone --recurse-submodules https://github.com/supertux/supertux
• Make the build folder: mkdir -p ./supertux/build/ && cd ./supertux/build/
• Run CMake: cmake ..
• Run make: make
• Make the package: cpack -G FREEBSD
  • This step will give a segmentation fault:

I tried re-running CPack with GDB, I get this:

It seems the problem happens at those lines in the FreeBSD libpkg; CPack is calling pkg from this line.

I'm not sure how to debug further; could anyone help me here?