WysiwygFormContainer/-Field not submitted in dialog

[mutec]

$messageContainer = WysiwygFormContainer::create('text');
$messageContainer->messageObjectType('foo');
$messageContainer->maximumLength(20000);
$messageContainer->supportMentions();
$messageContainer->supportQuotes();
$messageContainer->supportSmilies();
if (MODULE_ATTACHMENT) $messageContainer->attachmentData('foo', $this->parameters['parentObjectID']);

in the dialog form there's a wysiwyg editor supporting similies and attachments, but when I hit the submit button it's values aren't sent:

parameters[parentObjectID]: 85
parameters[data][title]: zterer
(empty) // tags-field which was empty for that request
parameters[data][labelIDs6]: 0
parameters[formId]: threadAdd

Did I miss something or is this buggy?