Here is solution for Bootstrap3: Use .col-xs-n always.
The reason is wkhtmltopdf didnt support css in @media block. In bootstrap3, only col-xs-n rule outside @media block.
I’ve checked the bootstrap2.3.2 css, seems spanN rules always be inside @media block.
So an ugly solution would be copied out all spanN rules into top level to another css file and included it into html.