Making changes to one element of a series doesn't overwrite all elements of the series

Problem: I created a lesson series of 10 lessons, with one instructor covering all lessons except for one, in which I assigned another instructor. When I needed to make a change to the series as a whole, it automatically saved the series with the original instructor for all dates, even though the change I had to make was unrelated. It would be better if all settings for each individual date were held intact when an unrelated element is changed on the series as a whole.