Using template hooks vs. manual insertion into template

[Cloud-Warrior]

Hello!

I added some custom options to usercp after I read this great tutorial https://vborg.vbsupport.ru/showthread.php?t=116155

Instead of manually editing a template like in this tutorial I wanted to use a template_hook in order to make a product that is easy install for others.

At first I inserted this code directly into the modifyoptions template (as suggested in the tutorial):

<fieldset class="fieldset">
	<legend><label for="cb_allowsioc">Export SHA1</label></legend>
	<table cellpadding="0" cellspacing="$stylevar[formspacer]" border="0" width="100%">
	<tr>
		<td>
			Export encrypted version of my e-mail address
		</td>
	</tr>
	<tr>
		<td><label for="cb_allowsioc"><input type="checkbox" name="siocbitoptions[allowsioc]" value="1" id="cb_allowsioc" $checked[allowsioc] />Export SHA1</label><input type="hidden" name="set_options[allowsioc]" value="1" /></td>
	</tr>
	</table>
</fieldset>

And everything worked fine.

But when I add the code to the hook global_start using

$template_hook[usercp_options_privacy] .= ' [same as above] ';

there is a problem:
When I look at the usercp, the checkbox is never checked - it remains empty even tough in the userinfo I can see a 1 where it should be.

Can anyone see where the problem is?