set_value default value not working

[eluser]Unknown[/eluser]
When i use set_value and supply it with a default value variable it show blank.

Code:

<?php echo form_textarea( array( 'name' => 'question', 'rows' => '5', 'cols' => '80', 'value' => set_value('question',$question)) )?>

And this is working

Code:

<?php echo form_textarea( array( 'name' => 'question', 'rows' => '5', 'cols' => '80', 'value' => $question )?>