CHtml::htmlButton does not create the content of the button, which kind of negates the reason for using the button tag 
.
The $label parameter is the content for an html button, so the fix I arrived at is to change line 408 in CHtml ( Yii 1.0.8 )
From:
return self::tag('button',$htmlOptions);
To:
return self::tag('button',$htmlOptions,$label);