We have received reports that when using the WYSIWYG editor in constructing a blast the box shrinks horizontally.
This issue has been resolved. Please email firstname.lastname@example.org if you experience any further unexpected behavior.
Our team is aware of this issue and currently working on improving this experience. As a temporary workaround, note that the content editor maintains it's size until the box reaches the top of the browser. This allows for shorter emails to be formatted.