The content within a mktEditable class element within an email template are ignored from any changes as they are considered to be "default content". Any content within these elements will not see any changes made to them based on changes to the template, and will only be seen when creating a new Email asset.
You can update an editable section to remove it's editable status, however this will remove any changes to the content done in any email.
You can see which elements can be classified as Editable here: https://docs.marketo.com/display/public/DOCS/Email+Template+Syntax