openproject/app/views/issue_relations/create.js.erb

jQuery('#relations #errorExplanation').remove();

<% if @relation.errors.empty? %>
  jQuery('#relations tbody').append("<%= escape_javascript(render :partial => 'issues/relation', :locals => { :relation => @relation }) %>");

  jQuery('#relation_issue_to_id').val('');
<% else %>
  jQuery('#relations table').after("<%= escape_javascript(error_messages_for(@relation)) %>");
<% end %>