I flew the same mission this afternoon, and tried tapping at various times to see if Litchi would add a waypoint where I tapped.
Once the Mavic started flying the mission, I could tap all I wanted and no waypoint would be added. I tried it several times while the mission was in progress. I also tried it after the mission had been completed and the Mavic was hovering at the final waypoint (as I had set it up to do), and nothing happened.
Then I tapped the folder icon again, selected the same mission, and tapped Load. When I tried zooming in on the map with a two-finger pinch, it added a waypoint in about the same location as yesterday. I suspect this is what caused the minor fly-away yesterday. Seems like every time I try to do anything with two fingers on the super-sensitive
Moverio trackpad, it interprets it as a tap.
A little scary that this can happen after you've loaded a mission. It must not actually send the mission to the aircraft until you give it the command to take off. At any rate, now that I know what happened I can watch out for it.