WordPress has a built-in tag stripper. If you want to preserve your imported tags, you need to alter the behavior of this stripper.
Actually, I have no idea to disable it, but managed to insert some additional tags into allowlist. You can find out $allowedposttags and $allowedtags in /wp-include/kses.php.
But I don’t recommend changing them directly. You may want to create my-hacks.php file and enable it in your admin page.
My my-hacks.php file looks like this:
<?php
define('CUSTOM_TAGS', true);
$allowedposttags = //copy it from kses.php and modify
$allowedtags = //as above
?>
PS: I don’t think it’s the best solution. Is there any better idea?
