Smarter Navigation Not working in 3.6 with Toolbox

Hi,
I have a theme based on Automattic’s toolbox and using wordpress 3.6 and Simple Navigation doesn’t seem to be working.

They place their post navigation code in their functions.php and I have changed

<?php previous_post_link( '<div class="nav-previous">%link</div>', '<span class="meta-nav">' . _x( '←', 'Previous post link', 'toolbox' ) . '</span> Previous Drawing' ); ?>
		<?php next_post_link( '<div class="nav-next">%link</div>', 'Next Drawing <span class="meta-nav">' . _x( '→', 'Next post link', 'toolbox' ) . '</span>' ); ?>

to

<?php previous_post_smart( '<div class="nav-previous">%link</div>', '<span class="meta-nav">' . _x( '←', 'Previous post link', 'toolbox' ) . '</span> Previous Drawing' ); ?>
		<?php next_post_smart( '<div class="nav-next">%link</div>', 'Next Drawing <span class="meta-nav">' . _x( '→', 'Next post link', 'toolbox' ) . '</span>' ); ?>

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But the previous and next links still won’t stay within the category.

I have tried it with permalinks set to %postname% and %category%/%postname%

Any ideas?

Thank you.

https://www.ads-software.com/plugins/smarter-navigation/