Within the files generated by Artisteer, don't you have something like this in the file sidebar-default.php, or sidebar-secondary.php (...or whatever is yours) ?
<?php ob_start();?>
<ul>
<?php wp_list_categories('show_count=1&title_li='); ?>
</ul>
<?php theme_wrapper($style, array('title' => __('Categories', THEME_NS), 'content' => ob_get_clean())); ?>
Here we can clearly see the title is passed to the function theme_wrapper() (and eventually translated). Maybe you modified this when tweaking your theme....
Don't see options to hide title directly from the Artisteer application, although.
If it doesn't solve your problem, you may consider asking directly to Artisteer forums, as you paid for this.