Mavericks: User no longer owner of Home folder and content

One of the Users (called: The_Problematic_User) of a Mavericks installed MacBook Pro is no longer owner of the Home folder and content. Here's what we've tried to no avail:

• restart computer and log in recovery mode (Command-r) and;
  • repair disk permissions,
  • repair disk,
  • with resetpassword (command line),
  • reset Home Folder Permissions and ACLs,
  • reset password,
• restart computer and log in single user mode (Command-s which is root access) and;
  • Strip ACLs on all account items with: chmod -RN /Users/username
  • response: chmod: Failed to clear ACL on file ...
  • Try to regain ownership of files and folders with: chown -R username:staff /Users/username
  • response: chown: username: illegal user name (where username was the user name of the user, obviously)
  • Try to assign ownership of files to root with: chown -R root:staff /Users/username
  • response: chown: /Users/username/*: Read-only file system (where * represents all the files and folders in the directory)

Another thing: when I ls -l /Users here is what I get:

• drwxrwxrwt 6 root wheel 204 Feb 24 10:53 Shared
• drwxr-xr-x+ 12 501 staff 408 Mar 21 17:16 A_user (with admin privileges)
• drwxr-xr-x@ 47 502 staff 1598 Mar 15 12:03 The_Problematic_User
• drwxr-xr-x+ 24 505 staff 816 Jan 10 15:11 Another_user

What is the @ doing instead of the + in the permissions of The_Problematic_User?

For info: The_Problematic_User does NOT have admin privileges

An erroneous extended attribute has been applied to this directory somehow, but it can only be removed using the xattr Terminal command. You should take a look at a brief explanation here. A more detailed question and answer can be found at this StackOverflow page.