It is great to navigate between tasks with up/down arrows and to "open/close" tasks with left/right arrows. Just fantastic keyboard control.
My suggestion is to use left/right arrows only for opening/closing tasks. Use tab to cycle focus through all the task details (and make it cycle so that when it reaches the last detail, it starts back at the first).
Currently, left/right arrows cycle thru details and open/close task. So right arrow opens the tasks and then cycles thru details. Thus to close the task, you have to hit left a bunch until you get back to the "top." If arrows and tab were differentiated, you could easily have the focus on a task detail and quickly close the task with left arrow.
Also related to this is how using tab disrupts arrow use. If tab can't be better controlled, maybe disregard its use and concentrate on other keys to fully navigate Toodledo.