file concerned:
.\class\xoopsform\themeform.php

what is wrong:
insertBreak($extra = '', $class= '') member function
--> got its logic wrong, will not display $extra at all

solution:
fixed here

function insertBreak($extra = '', $class= '')
{
$class = ($class != '') ? " class='$class'" : '';
if ($extra == '') {
$extra = "<tr><td colspan='2'$class></td></tr>";
$this->addElement($extra);
} else {
$extra = "<tr><td colspan='2'$class>$extra</td></tr>";
$this->addElement($extra);
}
}