I'm trying to add a default value to an HtmlEditorField in admin. I have it working on TextFields, but for some reason it just won't work on HtmlEditorFields.

Here's a snippet of my code, edited down to just the relevant bits:

<?php

class SiteConfigExtension extends DataExtension
{
    private static $db = array(
        'Message' => 'HTMLText'
    );

    public function updateCMSFields(FieldList $fields)
    {
        $fields->addFieldsToTab('Root.Main', array(
            $a = new TextAreaField('Message', 'Message', '<h2>Default Message...</h2>'),
        ));
        $a->setRows(5);

Any ideas?

By the way, this is a problem that keeps occurring for me in various scenarios (not just with HtmlEditorFields but also with DropdownFields for example), but I've been unable to pin down the cause - it seems quite random.