According to http://ez.no/doc/ez_publish/technical_manual/3_8/reference/modules/content/fetch_functions/keyword and http://pubsvn.ez.no/nextgen/trunk/doc/features/3.8/enhanced_keyword_fetch_function.txt

the keyword fetch function must support 6 sorting methods. In fact, the following two methods do not work:

• name
• class_name

tested on 3.8stable rev.17936

Steps to reproduce

For default eZP 3.8 + shop_site package installation:
1. Add an attribute of the "Keywords" datatype to your folder class (class ID = 1) and article class (class ID = 2)
2. Create a couple of articles and folder containing "computer" as a keyword
3. Use the following code in one of your templates:

{def $list=fetch( 'content', 'keyword',
                  hash( alphabet, 'computer',
                      classid, array( 1, 2 ),
                      sort_by, array( 'name', false() ) ) )}

            {foreach $list as $element}
                {$element.link_object.name|wash} <br />
            {/foreach}
            {undef $list}

You'll get an error.

However, if you put for example "modified" instead of "name", it works