I was able to test out a few things and now have additional information.
1 - When this event happens, you can see it coming because the last place you clicked before combat began will retain the "move here" cursor, and the character will move towards that point.
2 - I do not have a suitable save, but with this comes news of a fix: Saving the game before said character's turn then reloading will remove the cursor and fix the issue, but you have to see it coming.
3 - It seems to be any fight where there's no dialogue beforehand. So the first voidwoken ambush might be an ideal place to test this. Or if there is dialogue there and my memory totally fails me, another example I can think of is the group of 4 magisters + dog guarding the prison entrance to fort joy once you have your collar off. Or maybe the frogs in the back of the cavern, or the turtles on the beach.
4 - My habit of spamming click (old starcraft veteran) may have something to do with it. From my observations, it seems to happen that there's 3 phases to "begin combat". In what I'll call the "first phase", an enemy is spotted, all linked characters begin to move into position, and any existing movement command is removed. In the "second phase", when characters are actually moving into combat formation but before initiative order is displayed, it seems to remove character control but still accept movement commands, and in the "third phase", combat begins.
From what I've noticed, it appears that when I'm still clicking around when a fight starts, mostly due to being surprised by combat, and I happen to give a move order during the "second phase" of preparing for combat, it'll reproduce this issue.
