Description:
------------
get_defined_vars() only contains the $this variable entry when $this is assigned or returned. In all other cases (no use, gettting or setting of property, callign a method) the $this entry is missing from the list.

Test script:
---------------
// Full example is at http://pastebin.com/FDJzCTRG

class Test
{
 	//...
 	public function testNoThis() {
		echo __METHOD__ . PHP_EOL;
		var_dump(array_keys(get_defined_vars()));
	}
 	//...
}

$t = new Test();
$t->testNoThis();


Expected result:
----------------
Test::testNoThis
array(1) {
  [0]=>
  string(4) "this"
}
Test::testThisGet
array(1) {
  [0]=>
  string(4) "this"
}
Test::testThisSet
array(1) {
  [0]=>
  string(4) "this"
}
Test::testThisCall
array(1) {
  [0]=>
  string(4) "this"
}
Test::testThisUse
array(1) {
  [0]=>
  string(4) "this"
}


Actual result:
--------------
Test::testNoThis
array(0) {
}
Test::testThisGet
array(0) {
}
Test::testThisSet
array(0) {
}
Test::testThisCall
array(0) {
}
Test::testThisUse
array(1) {
  [0]=>
  string(4) "this"
}