Keep the calendar type when duplicating task instead of defaulting to default task calendar in my case TO-DO calendar.
The example in the image is a task set to use my main calendar, which I then duplicated, but the second task did not stay as main calendar and instead defaulted to the TO-DO calendar which i've set for all new tasks.
Personally I find it more intuitive, that when I duplicate something, it is the same as the origin.