[Mailpoet] text breaks in MailPoet email editor when Stackable setting to default Stackable paragraph is enabled

[malalacharm]

Describe the bug
MailPoet is transitioning to a block-based email editor. When Stackable's setting to default to the Stackable "Paragraph" block is enabled, the MailPoet email editor breaks: text cannot be pasted in or edited normally.

To Reproduce
Steps to reproduce the behavior:

1. Click on MailPoet > Emails > Add new email
2. Under the Newsletter section, click on the dropdown which should show Create using the new email editor (Alpha)
3. Paste content from Google docs: https://docs.google.com/document/d/19GD9jfWKuWQX5OnhULV4w076pTnVlmBG9JaD2sR1nv4/edit?usp=sharing
4. See error (text is not pasted, if using list, it becomes separated paragraphs)

Expected behavior
Content pasted into the MailPoet block-based email editor should be preserved and editable as expected, regardless of whether Stackable's "Use Stackable Paragraph as default" setting is enabled. Pasted text should retain its paragraph and list structure and allow user to continue editing without issues.

Screenshots