Sometimes during marine drop when I detect that coming opponent forces are overwhelming I am trying to get all marines back into Medivacs and go back to my base.
Usually I have marines and Medivacs in one group and when I need to go back I do right-click this group on each Medivac with 'shift' key pressed.
Usually one Medivac is fully loaded while all others are empty and 5-10 marines are left... I am trying to get them back into empty Medivacs (keep right-clicking on them), but that doesn't help: marines stay on the ground, medivacs don't go to them to pick-up.
Question: Why? What am I doing wrong?