The weirdest UX problem I've found with Mandrill is that you can't use the browser "CTRL-F" to search an email template unless the text is _currently_ visible. Not sure how they manged to mess up the search functionality for a text box that is intended to have massive amounts of text in it. It makes it harder to do a minor spot edit of a template than it should be. Things begin to make sense now...
I believe this is a performance optimization to limit what's actually in the DOM for large documents. The code editor is fairly common and is also used by Google Tag Manager, but it annoys the heck out of me too.
