There's a conflict happening on MailPoet when you enable Edit Flow. Somehow our TinyMCE stop working at all.
This conflict might be happening for more than 6 months: http://wordpress.org/support/topic/mail-poet-former-wysija-newsletter-conflict
MailPoet: http://wordpress.org/plugins/wysija-newsletters/ (any version)
Edit Flow version: 0.8
Video reproducing the issue: https://mailpoet.viewscreencasts.com/95107ca0caf50a002c1860437e48b322