Rated 4 out of 5 stars

I have been working on this problem for months on end. I reached a point where I returned to Outlook as this problem was killing my planning capabilities.
Last night I found the problem. A bunch of completed tasks imported from Microsoft To Do. How they have appeared in Thunderbird only Billy Gates know...
As soon as I deleted those tasks all problems disappeared.

This review is for a previous version of the add-on (3.0.2).  This user has a previous review of this add-on.