[Typo3-dev] Extending fe_users, what am I missing in the tutorial?

[Dani Eichhorn]

Happy new year everyone...

I'm trying to extend the fe_users table with some field, eg. a checkbox 
where the frontend user can tell if he is a student or not. I followed 
step by step the tutorial at
http://typo3.org/documentation/document-library/sr_feuser_register/Tutorial_Adding_fie-1/
but at the end, the front end registration form still shows the 
submarkers (this is the html source of the registration form):

	<!--###SUB_INCLUDED_FIELD_student###-->
	<tr>
	<td>

		<p>###LABEL_STUDENT### ###REQUIRED_STUDENT###</p>
	</td>
	<td>
		<p><font color="red" ><b><!--no error--></b></font></p>
		   <!--###SUB_REQUIRED_FIELD_student###-->
			<p><font color="red" ><b>###MISSING_STUDENT###</b></font></p>>
		   <!--###SUB_REQUIRED_FIELD_student###-->
		<p><input name="FE[fe_users][student]" type="checkbox" value="" /></p>

	</td>
	</tr>
	<!--###SUB_INCLUDED_FIELD_student###-->

In the template I added the following constants:

plugin.tx_srfeuserregister_pi1.formFields = [...the other fields...],student
plugin.tx_srfeuserregister_pi1.file.templateFile = EXT:sqx_pcumembers/form.html
plugin.tx_srfeuserregister_pi1._LOCAL_LANG.default.student = Student
plugin.tx_srfeuserregister_pi1._LOCAL_LANG.default.missing_student = This field is required!
plugin.tx_srfeuserregister_pi1._LOCAL_LANG.default.missing_invitation_ student = This field is required!

My own extension with the new fields works fine in the backend, I can add, edit and delete fe_user entries with the new fields,
so the TCA seems to be OK.
What am I missing here, why doesn't Typo3 replace the submarkers with the label/missing message?

Thanks
Dani