ntpd seems to ignore "disable kernel" directive in ntp.conf

The directive "disable kernel" in /etc/ntp.conf should, per my understanding, stop ntpd from adjusting the system clock using ntp_adjtime calls.

On Ubuntu Bionic LTS with ntpd v4.2.8p10, these directives seem to be ignored as the debug output of ntpd -d shows:

# ntpd -d
 8 Jan 21:30:51 ntpd[10906]: ntpd 4.2.8p10@1.3728-o (1): Starting
 8 Jan 21:30:51 ntpd[10906]: Command line: ntpd -d
 8 Jan 21:30:51 ntpd[10906]: Cannot set RLIMIT_MEMLOCK: Operation not permitted
 8 Jan 21:30:51 ntpd[10906]: proto: precision = 0.115 usec (-23)
Finished Parsing!!
[...]
newpeer: 127.0.0.1->127.127.1.0 mode 3 vers 4 poll 3 3 flags 0x29 0x1 ttl 0 key 00000000
 8 Jan 21:30:51 ntpd[10906]: start_kern_loop: ntp_loopfilter.c line 1119: ntp_adjtime: Operation not permitted
event at 0 0.0.0.0 c01d 0d kern kernel time sync enabled
 8 Jan 21:30:51 ntpd[10906]: set_freq: ntp_loopfilter.c line 1082: ntp_adjtime: Operation not permitted
event at 0 0.0.0.0 c012 02 freq_set ntpd 0.000 PPM

The output shows that ntp_adjtime is called in spite of the "disable kernel" directive in /etc/ntp.conf. Is this expected behavior?

Background: I'm running ntpd in a container. While it should serve time to other machines, it should not manipulate the system clock as the clock is managed by the container host.