On boot you see many copies of
/etc/network/if-up.d/ntpdate
	lockfile-create /var/lock/ntpdate

This is because of the ntpdate script, which runs for every interface.

To prevent this, add this to the top of /etc/network/if-up.d/ntpdate:
# Only update the date if eth0 goes up.
if [ "$IFACE" != eth0 ]; then
	exit 0
fi