Escape behaviour select vs insert

As I understand, strings passed to db->where() and db->insert() are escaped by default.  I see differing results passing strings containing ' and ' or ' or '.  insert() processes as expected though where() inserts unwanted whitespace.  I'm using CI 3.0.1.

PHP Code:

$col2 = 'foo and bar';
$this->db->select('col1');
$this->db->where(array('col2' => $col2));
$this->db->from('table1');        
$this->db->get();
echo $this->db->last_query() . "\n\n";
$this->db->insert('table1', array('col2' => $col2));
echo $this->db->last_query(); 


Code:

SELECT `col1`
FROM `table1`
WHERE `col2` = 'foo and  bar'

INSERT INTO `table1` (`col2`) VALUES ('foo and bar')

I'm unsure if this is a bug as such or misuse on my part.  What's the best approach in order to continue usiing the query builder as it's so convenient!  Right now I am simply removing duplicate whitespace before running the generated query:

PHP Code:

$this->db->query( preg_replace('/\s{2,}/', ' ', $this->db->get_compiled_select()) ); 


Any tips appreciated.