Hi,
I have found this bug also.
Its in the geraint template.
There is a typo in components/com_jevents/views/geraint/icals/tmpl/icals_form.php on row 135
else if ($jinput->get('categories', 0) && in_array($c->id, $hinput->post->get('categories', '', null)))
$hinput->post->get should be $jinput->post->get
Please fix this in next update.