Flight change issues
 

Hi all, I have a flight booked - CEB - TPE - CEB with the outbound in economy and return in business.

I need to change the date for the outbound flight, with the return staying the same, but when I try to change, it forces me to select again for both legs, with the business class portion on the return now at a much higher price, despite the fact I am not changing the return flight in any way. Is this the way it is supposed to be or is there a way to just change the first flight?