Trying to workaround prior bug #1140716, I added to my config:

  log-facility=/dev/null

Next thing I see after dnsmasq restart:

# ls -la /dev/null
crw-rw-rw- 1 dnsmasq root 1, 3 May 20 22:25 /dev/null

Suspected something like this could happen, so I checked.

Combined with the aforementioned bug, must admit I have not seen a piece of
software being this low quality at any time before in my life.