apparmor.vim contains interpolated make(1) status messages
See downstream bug: https://bugs.archlinux.org/task/65450
A long series of strange design decisions somehow led to python subprocess.Popen being used to run a Makefile that echoes content exclusively to stdout... and then the stderr from Popen is explicitly appended to stdout and used to do regular expressions when generating data files.
I won't comment on the rest, but there is no way create-apparmor.vim.py should ever be wanting to see stderr for any reason whatsoever. It's even directly contradicting its own docstring.