If we are high on profile , it shows the intercepting point , and then as we get closer it moves ahead over and over again;
I don't know how this is calculated on the A330 (rated on A320), but on the A320 this is the way the system is designed. If you are high on profile the intercept point is valid for a descend with half speedbrakes. So without speed brakes the intercept point will move forward. Not sure if its the same on the A330 but from your description it seems to be...