I've just had to make the third change on a CGK-SIN-AKL-SIN-CGK itinerary due to changing dates from work.

Each time the Jakarta sectors have been wide open in terms of seat selection and I select my normal seats.

However the SQ285/286/281/282 flights all show a total of 3 middle seat in the centre sections of economy available and that's it... every time!

Really odd.