PHPOffice/PHPExcel — pull request #94 by Slamdunk (2012-11-25 08:08:16+00:00)
Title: Use appropriate dereferencing

Array reference has the priority over key reference.
```php
$this->$key[$k] = 1;
// Is equal to
$key = $key[$k];
$this->$key = 1;
```
If you want to get the double dynamic reference, you need to use the Curly brackets.
```php
$this->{$key}[$k] = 1;
```

So now this test does not get errors anymore:
```
1) AutoFilterTest::testClone
Illegal string offset 'L'

/var/www/tmp/PHPExcel/Classes/PHPExcel/Worksheet/AutoFilter.php:837
/var/www/tmp/PHPExcel/unitTests/Classes/PHPExcel/Worksheet/AutoFilterTest.php:330
```