Comment 1 for bug 420098

I think you have slightly misdiagnosed the problem. /etc/rcS.d/* are run in all runlevels, not just single user mode. (Single user mode runs /etc/rcS.d/* and /etc/rc1.d/*; multiuser mode runs /etc/rcS.d/* and /etc/rc2.d/*.)

However, you seem to have the same symptoms as bug 448095, which is caused because resolvconf starts after ifupdown. I will mark this as a duplicate for now.