IMage Background not show in 3.6.4

Hello, last Friday when my site is updated from 3.5.7 to 3.6.4 the background image is not displayed.
I use a relative path in ATO-> Body-> Body Style

background: url('<?php bloginfo('wpurl'); ?> /wp-content/my-atahualpa/background/gerardo_buchmann.jpg') no-repeat center top;

When I changed to
background: url('/wp-content/my-atahualpa/background/gerardo_buchmann.jpg') no-repeat center top;

the image is displayed.

After updating another site on another server, the same problem occurred.
Please could you consider whether it is a problem of Atahualpa?

Please apologize for my English.
Marcelo