wp_dropdown_categories directs to Category base, not the actual category

I’m sure it used to work ok in a previous version – I haven’t worked out when it stopped.

I use wp-dropdown_categories to create a dropdown list of categories in the sidebar of my site.

When I pick a category & click on submit to go to the category, it takes me to sitename.com/category/ not sitename.com/category/categoryname where categoryname is the name of the category I’m choosing. In the permalink setting I have chosen category as the Category base setting.

As a result of this, whenever I try & select a category from the dropdown I just get a 404 error. Categories set at the end of posts are still working fine.

Has anyone else had this problem, or does anyone have any suggestions how to solve it?

My code that is producing the dropdown list is:

<form id="categories" action="<?php bloginfo('url'); ?>" method="get">
   						<h3>By category</h3>
						<p>
				<?php wp_dropdown_categories('orderby=name&hierarchical=1&hide_empty=1&show_option_none= '); ?>
				<input type="submit" name="submit" class="submit" value="View" />
				</p>

			</form>