Thank you for reaching out to us in the Community regarding the issue you're experiencing.
The pop-up is designed to come up when a non-mobile template is copied. I did a few tests in your account to try and replicate and it only came up when I made a copy of a non-mobile template.
But, it sounds like you're saying it comes up every time you go to edit a template, not just when you make a copy of the template.
We might have to do some additional troubleshooting to figure out how to resolve this. If you could e-mail us at social_support(at)constantcontact(dot)com with your username, the browser you're using, an example template, and a brief reference to this post. We'll investigate further.
It is possible this is a cache/cookies related issue. When I used my go-to browser Chrome to troubleshoot I was not able to get the pop-up to come up no matter what I did. It was only when I changed to Firefox, with a clean cache/cookie slate, that I got the pop-up to show. I would check to see if your browser is set to remove all cookies/cache after each use which might explain why the pop-up keeps showing.