Index: wp-includes/pluggable.php
===================================================================
--- wp-includes/pluggable.php	(revision 17565)
+++ wp-includes/pluggable.php	(working copy)
@@ -1502,6 +1502,11 @@
 
 	$check = $wp_hasher->CheckPassword($password, $hash);
 
+	// if $password is at least double slashed and check failed, try again with one level of slashes removed.
+	if (!$check && false !== strpos($password, "\\\\")) { 
+		$check = $wp_hasher->CheckPassword(stripslashes($password), $hash);
+	}
+
 	return apply_filters('check_password', $check, $password, $hash, $user_id);
 }
 endif;