This bug exists in PHP version 4.1.2 - 4.3.1 and 5.0.0-dev.
It is similar to bug #18872 (Improper handling of class constants used as default function argument values).

See the following PHP code:

<?php
  function f($a=array(PHP_VERSION=>PHP_VERSION)) {
    print_r($a);
    echo "<br>\n";
  }
  f();
  f();
?>

The function "f" should print the same result at first and at second invocation but it is not true. The output is:

Array
(
    [4.3.1] => 4.3.1
)
<br>
Array
(
    [PHP_VERSION] => 4.3.1
)
<br>

The error is in handling of "ZEND_RECV_INIT" opcode and in
function "zval_update_constant" that resets "IS_CONSTANT_INDEX" flag in original "zval" instead of copy.