Why don't Marines get back into Medivacs?

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?

The problem here is that your marines and medivacs are in the same group.

When marines and medivacs are selected, and all medivacs are empty, right clicking a medivac will tell the marines to go in. When at least one medivac is full, the default action on right clicking will be to tell all units to move to that medivac (default action for the full medivac apply to the whole group).

Try having marines and medivacs in two separate groups (1 and 4 for example), double tap 4 to focus your medivacs, press 1 to select marines, shift right click right click right click, and when they're all loaded press 4 and fall back :)

EDIT: You can also select your group, right click a medivac, hit tab to select the medivacs, then press the shortcut 'load' instead of relying on the right click default action, that should work too :)

If you prefer not breaking up into multiple control groups, SHIFT+CTRL+Leftclick on a medivac icon in your group display before trying to load. That's an easy way to get the medivacs deselected, so you can use your current 'right click on the medivacs' method to load the rest of your unit mix