it only happens when you edit the text in the rich text editor?
i am guessing that the problem is there. how are you incorporating these modules?
are there any closing tags in it that would prematurely close something else?
when i build my email templates, i use custom modules, then copy the module snippet and add to my email template. roughly like this:
<table>
<tr>
<td>
{% module "module_154360243717279" module_id="1596258" label="Content" %}
</td>
</tr>
</table>