Ditzy is correct. The reason the seats are locked upright at the exit rows is because they do not meet the minimum pitch requirements set by CASA for windows exits. An exemption was therefore given to Jetstar provided that the said seats remain locked upright at all times. This was discovered during the A320 proving flights with CASA. You will notice also that the seat cushions at the exit rows are also shorter than the other seats, to squeeze out a couple more inches in the pitch.