Doing unset() on a static variable causes it to forget the fact that it is static for the rest of the function.

e.g.

<?
function abc() {
  static $a = 123;
  echo "On entry, a = $a\n";
  unset($a);
  $a = 456;
}

abc();
abc();
?>

should give 123 then 456. It gives 123 and 123.

Replacing unset($a) with $a = null, or removing the unset() entirely has the desired result of giving 123 then 456.