I'm wondering why sudo -i doesn't start a shell as root.
$ wget http://tinycorelinux.net/8.x/x86_64/release/CorePure64-8.2.iso
$ qemu-system-x86_64 -cdrom CorePure64-8.2.iso -m 512
# press enter for no boot codes
$ id
uid=1001(tc) gid=50(staff) groups=50(staff)
$ sudo -i
$ id
uid=1001(tc) gid=50(staff) groups=50(staff)
$
It seems the sudo version is old.
$ sudo -V
Sudo version 1.7.8p1