[Rails] Strange custom field error message behavior

I'm developing with ruby 1.9.2 and rails 3.2.2. Currently I want to customize the error message html, to place the error message below a text area. But what it behaves is two message box around the text area. Do you know where the problem is? Thanks.

ActionView::Base.field_error_proc = Proc.new do |html_tag, instance|
errors = instance.error_message
errors_list = "<ul>" + errors.map { |e| "<li>#{e}</li>" }.join + "</ul>"
%(#{html_tag}<section class="validation-error"><h2>Errors</h2>#{errors_list}</section>).html_safe
end

<section class='field' id='content'>
<label for="script_content">Content</label>
<section class="validation-error"><h2>Errors</h2><ul><li>can't be blank</li></ul></section>
<br>
<textarea cols="40" id="script_content" name="script[content]" rows="20"></textarea>
<section class="validation-error"><h2>Errors</h2><ul><li>can't be blank</li></ul></section>
</section>

Best regards,
Zhi-Qiang Lei
zhiqiang.lei@gmail.com