Had the same issue using TinyMCE 4.3.3, Revo 2.2.10-pl. Found that template content is stripped when it contains HTML attribute class.
For example, my template contained:
As usual - it showed up in preview, but after clicking Insert button everything was gone. Nothing really was inserted.
After removing class atribute, my template looked like this:
This was working fine. But didn't satisfied my needs. I desperately needed a template with class attribute.
Found a solution. You need to provide some class name for this setting: tiny.template_selected_content_classes
It's empty by default and that's why template content is stripped. When you enter some CSS class name (I used fake one), everything works great again. So my setting looked like this:
Important! Dot (.) before class name is the key. When using class name like this: fakeCssClass (without dot in front), nothing worked.
Hope this helps!