This is actually a bug that we are looking into now. Sorry about that.
This issue has been fixed, but requires deleting Todoist's offline cache. This can be done:
In Chrome - go to Advanced Settings -> Content Settings -> All cookies and site data, find and delete all Todoist-based entries on this list.
In Firefox - go to Options -> Advanced -> Network and delete Todoist-based entries from the list of sites storing offline data.
In Outlook or the Windows app, delete the "Cache" folder located in C:\Users[username]\AppData\Local\Todoist\Windows ... or \Outlook.