Thank you for bringing this to our attention! I apologize you are having this experience with working in your email campaign, it is definitely not the experience we want our users to have. I have taken a look at your most recent campaign and was unable to replicate the same experience. Is this happening to your in more than one campaign? Or even more than one block?You are however still working in our previous Legacy Editor campaigns. We have seen cases where copying and reusing a template in this editor too often or too much can cause formatting issues. Are you copying a previous email or creating a brand new one? If you are copying an email that has been reused often I would suggest testing a new email through the Create button to see if this experience still occurs.
Testing your campaign in a different browser or a private/incognito window is also a great troubleshooting step to take. Doing this helps determine if there are any 3rd party add-ons that could affect how Constant Contact works.