I am getting the following error message when multiple attributes are selected in a category listing and pagination is clicked.

ERR (3): Warning: strlen() expects parameter 1 to be string, array given  in /home/site/public_html/app/code/core/Mage/Catalog/Model/Layer/Filter/Attribute.php on line 94 

The error relates to this block of code:

    public function apply(Zend_Controller_Request_Abstract $  request, $  filterBlock) {     $  filter = $  request->getParam($  this->_requestVar);     if (is_array($  filter)) {         return $  this;     }     $  text = $  this->_getOptionText($  filter);     if ($  filter && strlen($  text)) {         $  this->_getResource()->applyFilterToCollection($  this, $  filter);         $  this->getLayer()->getState()->addFilter($  this->_createItem($  text, $  filter));         $  this->_items = array();     }     return $  this; } 

I understand strlen only counts a string but can anyone tell me

1. Why it could be getting an array
2. Is this a bug in Magento (1.9.3.7)
3. How to fix?