Conditional Field Group showing up, although condition not met

Hi there,
I'm trying to set up a CRED form. There is a checkbox ("forum") – when it is clicked I want a set of radio buttons ("buchungsart-forum") to show up. I created all the fields via types and followed your instructions on how to insert the conditions in the form editor.

Resulting is the following code:

		<div class="cred-field cred-field-forum">
			<div class="cred-label">Ich möchte am Forum teilnehmen</div>
			[cred_field field="forum" post="ticket" value=""]
		</div>

[cred-show-group if="($(forum) eq  '1' )"  mode="fade-slide"]
		<div class="cred-field cred-field-buchungsart-forum">
			<div class="cred-label">Art der Buchung Forum</div>
			[cred_field field="buchungsart-forum" post="ticket" value=""]
		</div>
[/cred-show-group]

It looks to me as if it should be working finde, but the radio buttons shows up all the time, no matter what.

What am I possibly missing there?

Thanks in advance!
Angela