Hi,
If you are visiting any particular category, the "Search" module searches the product within that specific category. It is a feature, but yes you are right. It might cause some other problem (like: not being able to find all products)
To eliminate that filter, (so the search will always search products within whole site)
open this PHP file:
/templates/YOUR_TEMPLATE/html//mod_virtuemart_search/default.php
look for this line:
<form action="<?php echo JRoute::_('index.php?option=com_virtuemart&view=category&search=true&limitstart=0&virtuemart_category_id='.$category_id ); ?>" method="get">
and replace it with this:
<form action="<?php echo JRoute::_('index.php?option=com_virtuemart&view=category&search=true&limitstart=0' ); ?>" method="get">
and you will be good to go.
Regards,
Support