The way Subtasks are handled in Toodledo is the main reason I don't use Toodledo as much as I would like.
Requests to make Subtasks user-configurable to always show them nested for more than a year now have gone unheeded. Anything you do at all in Toodledo causes the subtasks to become "un-nested", requiring another click on the toggle link. Can't tell you how many times I hit the Print button just before realizing that the subtasks are not where I need to see them. And that is after clicking the Toggle button at least a couple dozen times while working on my task list for maybe ten minutes.
I think it is safe to assume that this behavior will never be fixed. Oh well.