ls ignores LC_COLLATE in sorting of files

The "ls" command does not honor the LC_COLLATE setting. Steps to reproduce:

1) In an emtpy directory type "touch a b; mkdir x"
2) Do: "ls -l"
3) Then: "export LC_COLLATE=C"
4) Again: "ls -l"
5) Expected was that directories are outputted first but nothing changes.
6) Setting LANG=C or LC_ALL=C does not help either.

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Description: Ubuntu 16.04.1 LTS
Release: 16.04

coreutils:
  Installed: 8.25-2ubuntu2
  Candidate: 8.25-2ubuntu2
  Version table:
 *** 8.25-2ubuntu2 500
        500 http://de.archive.ubuntu.com/ubuntu xenial/main amd64 Packages
        100 /var/lib/dpkg/status

Thank you!