Hi,
When entering a repeating task using time, it would seem more logical that the default time where duration starts from is the start date, not the due date. This in part because the start date and time are at the top in the dialog box... so mainly a usability thing. I have for years struggled with this, since I do not often create repeating tasks, but everytime, I have to click, change, try, change, etc before I get the lead time right.
Think about it, and see if its a worthwhile small change that maybe will make the use of this particular aspect easier.
Cheers, Grant