Every item in my 'To Do List' suddenly has a duplicate--why?

[cagross99]

TL;DR I just added a new Exchange account to Outlook, and as an immediate result, all of the existing items in my 'To-Do list' were duplicated (screenshot). Any ideas why this happened, or how to resolve it?

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For the past several years, I have used Outlook 2013 (Windows 10) to manage my email, calendar, and tasks. I've had several IMAP email accounts for my email. My calendar/tasks were stored in a single PST file on my computer. If I open Tasks-->'Tasks' view, it would show all my tasks, both completed and in-progress. If I open Tasks-->'To-Do list' view, it would show all my in-progress tasks. To Outlook, I just added a new Exchange account (Office365), which I thought would be for email only. I can now manage that email account in Outlook, as expected/desired. But when I now open Tasks-->'To-Do list' view, it shows a duplicate of every entry in the list (screenshot). Any ideas why, or how to remove the duplicates?

• If I delete entry in the To-Do list, its duplicate entry is also deleted.
• If I create a new entry in the To-Do list, a duplicate is automatically created.
  
• If I open Tasks-->'Tasks' view, there are no duplicates (screenshot).
• In my Reminders window, there are no duplicates (screenshot).
• If I open Calendar, there is still only one calendar displayed--there are no duplicate entries of any kind there.
• I tried to reset my Outlook Task view, but that didn't do anything.

Thanks in advance.

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