Help--goal subtasks disappeared when moved from previous week

I had many subtasks listed under my goals but when I switch them from week to week or "remove the week" from within the goal, it deletes all subtasks. So much work is lost. I don't understand how I should be storing the steps in a project so that I can assign one step/task to a particular day but then keep the rest of the list to use for a future time. Where is there more information on how to keep projects organized by smaller tasks? Is this supposed to be in a Parking Lot list even when the project is a high priority, active project?