Движок указанной функцией обрезает теги, например здесь system/Content/Search/Index
/* Strip spoilers */
$content = $object->searchIndexContent();
if ( preg_match( '#<div\s+?class=["\']ipsSpoiler["\']#', $content ) )
{
$content = \IPS\Text\Parser::removeElements( $content, array( 'div[class=ipsSpoiler]' ) );
}
/* Take the HTML out of the content */
$content = trim( str_replace( \chr(0xC2) . \chr(0xA0), ' ', strip_tags( preg_replace( "/(<br(?: \/)?>|<\/p>)/i", ' ', preg_replace( "#<blockquote(?:[^>]+?)>.+?(?<!<blockquote)</blockquote>#s", " ", preg_replace( "#<script(.*?)>(.*)</script>#uis", "", ' ' . $content . ' ' ) ) ) ) ) );