After losing a unit due to injury (not dead just wounded) i decided to do a second crashsite that just had formed. While the dropship was heading to the other crashsite,i was able to add an 8th soldier back to it, while it hadnt reach the base. I figured it would not show up in my dropship on mission start, but surprisingly it did.
So due to a bug, i was able to add a soldier to my dropship, while it was still flying.