Could be because of these udev rules. I would say this makes it a bug.
Perhaps rebuildfstab should also check if NOFSTAB is set.
/etc/udev/rules.d/98-tc.rules:ACTION=="add", SUBSYSTEM=="block", RUN+="/bin/sh -c '/usr/sbin/rebuildfstab'"
/etc/udev/rules.d/98-tc.rules:ACTION=="remove", SUBSYSTEM=="block", RUN+="/bin/sh -c '/usr/sbin/rebuildfstab'"