This code crashesh php (tested via php-cli). When $i less-then condition is set to 100, this code works, but when is greater, it crashes on exit.

$content = '<?xml version="1.0" encoding="utf-8"?>

<auth xmlns:dt="http://www.nowhere.pl/">

  <dt:shadow name="rules" desc="Rules" zygryf="label"/>  
  <rules>

    <dt:shadow name="rule" desc="Rule" multiple="1" required="0"/>
    <rule>

      <dt:shadow name="expr" zygryf="text" desc="Match Expression" zygryf-size="40"/>
      <expr/>

      <dt:shadow name="group" desc="Group" multiple="1" required="0"/>
      <group>

        <dt:shadow name="name" zygryf="text" desc="Name" zygryf-size="20"/>
        <name/>
        <dt:shadow name="read" zygryf="bool" desc="Read"/>
        <read/>
        <dt:shadow name="write" zygryf="bool" desc="Write"/>
        <write/>
  
      </group>
    </rule>
  </rules>

  <dt:shadow name="default" desc="Default Rule" zygryf="label"/>  
  <default>

    <dt:shadow name="group" desc="Group" multiple="1" required="0"/>
    <group>

      <dt:shadow name="name" zygryf="text" desc="Name" zygryf-size="20"/>
      <name/>
      <dt:shadow name="read" zygryf="bool" desc="Read"/>
      <read/>
      <dt:shadow name="write" zygryf="bool" desc="Write"/>
      <write/>

    </group>

  </default>

</auth>

';

print microtime() . "\n";

$dom = domxml_open_mem($content);

for ($i = 0; $i < 300; $i++) {
  $dom = domxml_open_mem($content);
  $context = xpath_new_context ($dom);
  $results = xpath_eval_expression($context,"//*[name() = 'dt:shadow'][@zygryf='text']");
  unset($dom);
  unset($context);
  unset($results);
  }

print microtime() . "\n";