Sorry to drudge this thread up again, but I just discovered something interesting... an EAS bug on the iOS side, showing that it's not all perfect, peachy-keen happy love over there.
For what it's worth, I've been using my iPhone 4S as my primary phone instead of my Lumia 820. (I love my 820 and carry with my in my laptop bag, but I require certain apps which are only available - or only work - on iOS. But that's an issue for another thread.) So I'm sitting at work and a spam message comes into my Outlook (and thus my iPhone as well). On Outlook, I right-click it, point to Junk, and select Block Sender; this moves the email to my Junk E-mail folder. From there, I right-click the Junk E-mail folder, select Empty Folder, and the email is gone. A few minutes later, I pick up my iPhone and the spam message is at the top of my email, unread. I pull down to refresh, but it remains. I check Outlook, it's not there. So I swipe over the email on my iPhone and the Delete button comes up, which I tap, and the message is deleted on my iPhone... but, suddenly, the message shows up in the Deleted Items folder on Outlook again. After I've already junked it and deleted it once in Outlook, my iPhone brought it back from the dead.
Must be a glitch, right?
Well, about an hour later I received another spam message. So I try it again, using the same steps: junk it on Outlook, empty Junk Email folder, check iPhone... the message is still there. Swipe delete it on the iPhone, it shows back up in the Deleted Items folder on Outlook.
So, yeah, as far as I can tell, this is a reproducible error using Exchange Server 2010, Outlook 2010, and an iPhone 4S running iOS 6.0.1 syncing my Exchange account. At some point I'll put my SIM back into my 820 and see if the same issue shows up on WP8 and report back here.