Description:
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I believe a problem with memcache reveals a problem with PHP. (PECL Memcache bug: http://pecl.php.net/bugs/bug.php?id=14239)

A call to memcache changes the parameter variable to 'string' type. The PHP problem is that this conversion is passed to ancestor and decendent copies of the variable, even through function calls, even though passed by value, not reference.

This appears to be similar to PHP Bug #42813, closed as Bogus. This is a newly compiled PHP installation using latest PHP, PECL, memcached.

Reproduce code:
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$value1 = 1.2;
$value2 = $value1; // this value is being passed -- all get modified
$value3 = $value2;

echo '<br>1 ' . gettype($value1) . ' / ' . gettype($value2) . ' / ' . gettype($value3);
set('asdf', $value2);
echo '<br>4 ' . gettype($value1) . ' / ' . gettype($value2) . ' / ' . gettype($value3);

function set( $key, $valueA ) {
  $valueB = $valueA; // this value is being passed -- all get modified
  $valueC = $valueB;
  
  echo '<br>2 ' . gettype($valueA) . ' / ' . gettype($valueB) . ' / ' . gettype($valueC);
  
  $m = new Memcache();
  $m->addServer('localhost');
  $m->set($key, $valueB);
  
  echo '<br>3 ' . gettype($valueA) . ' / ' . gettype($valueB) . ' / ' . gettype($valueC);
}

Expected result:
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Even when memcache bug corrupts $valueB, others should not be affected:

1 double / double / double
2 double / double / double
3 double / string / double
4 double / string / double

Actual result:
--------------
1 double / double / double
2 double / double / double
3 string / string / string
4 string / string / string