Copied from someone who posted this at UserVoice:
If you export a todo.txt on each save, and import everytime before you save, it gets a stupid bug.
- Delete a Task
2a) the old version todo.txt gets imported, which still includes the deleted task
2b) the deleted Task appears again in TaskCoach
- a new version of the todo.txt gets exported
- the deleted task, now have to be deleted in the todo.txt first, before it can be deleted in taskcoach. ...
So it would be better to import only on startup.