Show Completed Tasks Not Working

[strange_cathect]

I have many tasks that I complete, but for record keeping purposes I need them to remain visible. So, I've ticked the "Show Completed Tasks" box. If I mark a task complete, a line is drawn through it, as expected. But after I reboot the task is gone. Poof! I'd like these tasks to stay visible until I choose to delete them, which is how I think it is supposed to work. Any ideas here?

I run Thunderbird 38.5.1 on Ubuntu Linux with Lightning 4.0.5.2.

Thanks.

[ssitter]

Maybe you have you applied a filter to the task list, e.g. to show only open tasks? Click on empty area in task list to open the context menu and verify the selected filter.