I have a similar problem and also asked this question in another thread. I just found this on the website:
Once I have applied into one academic program in SIS, can I change my field?
As admission decisions are specific to each program, students cannot change their programs during the admission process. Once admitted to a program/field, a student must stay in that program for one semester, at which point he or she can request a field transfer. Field transfer applications are handled through the Graduate Advising Office.
Don't know if it happens often though. If I get an answer in the other thread--I will post it here!