Characters self-exit tasks?

I've noticed this too, but it's usually on the last tasks I set up. I think that if you set it to perform a task, then leave the game right away, the tasks performed after the last autosave/syncing of the game are lost and those characters/tasks resort back to previous state. I always do farm planting and broadcasting as my last tasks and those are the ones that are most often in the same situation you described.
I try to get everything going and then hit up the 6 second houses or go to Krustyland, to allow it enough time to sync on it's own.