With “magic quotes” disabled, why does PHP/WordPress continue to auto-escape my POST data?

I think I found it. Problem (bug): http://core.trac.wordpress.org/ticket/18322

Solution: http://codex.wordpress.org/Function_Reference/stripslashes_deep

    $_GET       = array_map('stripslashes_deep', $_GET);
    $_POST      = array_map('stripslashes_deep', $_POST);
    $_COOKIE    = array_map('stripslashes_deep', $_COOKIE);
    $_SERVER    = array_map('stripslashes_deep', $_SERVER);
    $_REQUEST   = array_map('stripslashes_deep', $_REQUEST);

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Note: As suggested by @Alexandar O’Mara, you might want to reconsider overwriting the superglobals like this. If it’s appropriate for your situation, for example, you might just “strip locally” using an alternative like $post = array_map('stripslashes_deep', $_POST);

Also see @quickshiftin’s excellent answer.