There are two locations for setting a default term. On the academics tab, this sets the default for displays of data (Exams, Grades, Courses, etc.). On the Registration page, this sets the default for search for class search and registration. The two settings can be, and quite often will be, different.
We have been asked why we make students set their own default term. We do not always know what data a student wants to view at any given time. Fall is easy, the vast majority of students want to view data in Fall. However, come April-August that is more difficult to calculate. Some students will have classes in Summer 1 and/or Summer 2, in addition to classes in Fall, while some prefer the display to remain on Spring for late grade additions. Many of our Graduate/Professional students teach courses as well as enroll in their own courses. Their needs for setting a default term are quite different than other students.