MailChimp Block: form labels appear when not in WordPress context (RSS feed, WordPress.com Reader)

[pauloeaquino]

Steps to reproduce

1. Start a new post (Site -> Posts -> Add New)
2. Add a MailChimp Block to the post, then publish.
3. View post in the Reader

What I expected

I expected to not see any part of the form and its associated debug notifications at all, since the post is being viewed in the Reader.

What happened instead

Instead, all status/alert messages of the MailChimp block were shown, i.e. "Processing…", "Success! You're on the list.", "Whoops! There was an error and we couldn't process your subscription. Please reload the page and try again."

Browser / OS version

Firefox, Chrome / MacOS Catalina version 10.15.4

Screenshot / Video

Context / Source

Originally discovered through #manual-testing when publishing a personal post

[simison]

This would likely show up via any RSS reader or when page/post is sent via email.