Those buttons show all the blog categories and 'default' is shown when a blog has no category, so you have 500 'uncategorised' blogs!! Unfortunately the word 'default' is hard coded within the Blog module and I'm thinking that it should be part of the module's language set so that users can change it if they want to. I'll get the module updated to do that.
Alternatively, the module's item_list.tpl template could be modified to exclude that button - replace line 23
<a href="{$_c.url}"><div class="stat_entry_box"><span class="stat_entry_title">{$_c.title}:</span> <span class="stat_entry_count">{$_c.item_count}</span></div></a>
with
{if $_c.title != 'default'}
<a href="{$_c.url}"><div class="stat_entry_box"><span class="stat_entry_title">{$_c.title}:</span> <span class="stat_entry_count">{$_c.item_count}</span></div></a>
{/if}
hth
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Paul Asher - JR Developer and System Import Specialist