I have a somewhat same but different situation.
I have two Outlook accounts, one my primary account (with a primary alias of outlook.com.au) that I use to login to my phone, desktop, tablets and xbox etc., then I have me secondary account (outlook.com). I've noticed some information not syncing correctly so I checked my details.
I noticed my Primary account only has the Email selection within the Outlook Sync settings on my 1520 (DP with Denim), and my secondary outlook account has all Email, Contacts, Calendar and Tasks available for syncing (see screenshots).. anyone seen this before and have a solution?

