In the file catalog/view/theme/default/template/module/searchanise.tpl replace the line:
location = $('base').attr('href') + 'index.php?route=product/search&search=' + encodeURIComponent(search);
with:
location = $('base').attr('href') + 'index.php?route=product/search&search=' + encodeURIComponent(search) + '&filter_name=' + encodeURIComponent(search);
This issue should already be fixed in the latest version of the OpenCart extension.