I’m having the same issue but have some specific interesting aspects:
1. The add media button works (and then b, i, link, etc buttons appear) when adding a NEW post but not when editing a post (or a draft).
2. Deactivating ALL plugins and using the default (twentyfourteen) theme makes no difference.
Does anyone have any thoughts?
I’m having the same issue. It redirects me to the Constant Contact page and makes me re-enter my email address…
