Description:
------------
The script below illustrates the issue.

Test script:
---------------
<?php
DEFINE('FOO', false);

if (@BAR) {
  echo "this is wrong.";
} else {
  echo "this is correct.";
}


if (@FOO) {
  echo "this is wrong.";
} else {
  echo "this is correct.";
}

var_dump(@BAR);

Expected result:
----------------
this is correct.this is correct.NULL

Actual result:
--------------
this is wrong.this is correct.string(3) "BAR"