Comment # 1 on bug 1075239 from Patrick Schaaf

Just noticed the same thing, fresh tumbleweed install on x86_64, /sbin/sysctl
from package procps-3.3.12-9.2.x86_64

For the older, working versions, stracing a "sysctl -w
net.ipv6.conf.all.disable_ipv6=1" shows:

open("/proc/sys/net/ipv6/conf/all/disable_ipv6", O_WRONLY|O_CREAT|O_TRUNC,
0666) = 3
write(3, "1\n", 2)                      = 2

For the broken, tumbleweed-current /sbin/sysctl I instead see:

openat(AT_FDCWD, "/proc/sys/net/ipv6/conf/all/disable_ipv6", O_WRONLY|O_TRUNC)
= 3
lseek(3, 1, SEEK_CUR)                   = 1
write(3, "0\0", 2)                      = 2

Observation: the broken one does not write a newline, but instead a nul byte.

Meanwhile, /usr/lib/systemd/systemd-sysctl as used during boot, keeps working
fine (i.e. changes to /etc/sysctl.conf become active on next boot)