mmm-mode/html-mode/php-mode issues

[Yuri D'Elia <wavexx@users.sf.net>]

Hi everyone. I'm having some problems when using php-mode as a submode
of html-mode.

I'm using emacs 23.1, and this is my relevant config:

(mmm-add-group
  'mmm-html
  '( (html-php-embedded
       :submode php-mode
       :face mmm-code-submode-face
       :front "<[\?]"
       :back "[\?]>") ))

(add-to-list 'mmm-mode-ext-classes-alist
  '(html-mode nil mmm-html))

I use html-mode on php files. mmm-mode correctly switches
the relevant parts to php, but when I type [tab] I get:

Wrong type argument: stringp, nil

A file as short as

<?php
test
?>

will trigger the error. Is php-mode not playing nice with mmm-mode?
How this can be fixed?

I don't really want to use mumamo/nX*.

Thanks