I have the similar experiences with KA (but they are changing the second leg of my trip which is run by CX) - the version of story I heard is in order to get me the emergency exit seat she would need a special code from Supervisor which led to a 5 mins wait - she certainly didn't need it before the system upgrade. She also reminded me that just in case I change the seat assignment online myself, I won't be able to go back to the exit seat assignment - I would have call again to fix it.