I'm sorry, the example was wrong, this is the right example:
<?php
class ExampleSuperclass
{
private $foo;
function propertyExists()
{
return property_exists($this, 'foo');
}
}

class ExampleSubclass extends ExampleSuperclass
{

}

$example = new ExampleSubclass();
var_dump($example->propertyExists());
?>

Another more complete example here:
<?php
 
class ExampleSuperClass
{
    private $foo;
    static protected $bar;
 
    private function foo()
    {
    }
 
    public function propertyFooExists()
    {
        return property_exists($this, 'foo');
    }
 
}
 
class ExampleSubClass extends ExampleSuperClass
{
    public function methodExists()
    {
        return method_exists($this, 'foo');
    }
 
    public function propertyBarExists()
    {
        return property_exists($this, 'bar');
    }
}
 
$example = new ExampleSubClass();
var_dump($example->methodExists());
var_dump($example->propertyFooExists());
var_dump($example->propertyBarExists());

?>

In php 5.2.1 you get:
bool(true)
bool(true)
bool(false)

php bool 5.3:
bool(true)
bool(false)
bool(true)

expected result: 
bool(true)
bool(true)
bool(true)

Using class name instead of object shows the expected result. I'd guess (according to docs) it should be same in both ways though.

This bug has been fixed in SVN.

Snapshots of the sources are packaged every three hours; this change
will be in the next snapshot. You can grab the snapshot at
http://snaps.php.net/.
 
Thank you for the report, and for helping us make PHP better.