@Jojo didn't notice your edit but no am not seeing the problem.
uhm, did see a difference in the code.
In jem 2.1.5 the image field is like
Code:
<fieldset class="panelform">
<ul class="adminformlist">
<li><?php echo $this->form->getLabel('datimage'); ?> <?php echo $this->form->getInput('datimage'); ?>
</li>
</ul>
</fieldset>
but in your file it's like
Code:
<fieldset class="form-vertical">
<?php
echo $this->form->renderField('datimage');
?>
</fieldset>
doing so will give a bit different code but can't tell right now if that's the problem. Maybe the css is messing with it.