/common_files/customer/main/subcategories.tpl
Code:
{if $smarty.get.page lt 2}
{if $current_category.description ne ""}
<div class="subcategory-descr">{$current_category.description|amp}</div>
{/if}
{/if}
wrap those if tags around the description and see what happens. for me it is near line 20.
This should get the page number from the url, if it is higher than 1 the description should not be displayed.