Hello,
when i create a new newsletter from a newsletter_type where "Allowed output formats" is only HTML, then in the newsletter creation phase (content/edit) always Text is selected.

My suspicion is that the code in
extension/ezxnewsletter/design/standard/templates/ezxnewsletter/edit_newsletter_object.tpl

          {foreach $newsletter.output_format_name_map as $value => $name}
        <option value="{$value|wash}" {cond( $newsletter.output_format|explode(',')|contains($value), 'selected="selected"', '')}>{$name|wash}</option>
          {/foreach}

will produce the problem.
After i inserted an attribute show on $newsletter.output_format, the output is always empty.