@esmi — Really? Sorry, but this has hardly gone unnoticed among WP users. There are multiple forum threads going back three years and more about TinyMCE (or whatever drives the editor) stripping ‘unwanted’ markup from posts. There seems to be no will to fix it however. I’m giving up and looking for a plug-in editor to replace the default.
Supposedly due to having <? rather than <?php on line 462 of tumblrize.php. Edited it and it worked for me.