[EDIT 2]
I do not have any idea for other languages but it could be happened for them too.
Specifically, Korean should stroke more than a single key when you want to finish 'a' character.
Precisely it ranges from 2-6 strokes.
Some of them are good enough for 2 strokes on the contrary others need more than that.
So, If you finish (User side) it in the middle of that and moves caret into another place.
SDL should be sunken into this problem (the other Editors do not know this one).
SDL moves the unfinished (Editor side) character together with caret into the new place.  

[EDIT 1]
It looks like that it is deeply intermingled with the characteristics of Korean.
-when a single agglutinative character of Korean is not finished (at Editor side) yet,
the user is tried to move active caret into another place.
But, I've never seen this unwanted phenomenon at any other editors except SDL Trados Studio.

The story goes like this.

At first stage, I was working at Red circle,
Next moment, I found that I needed to edit Blue circle,
So, I moved to Blue circle and added a character (Korean) "여" there.
Now, I came back to the Red circle and tried to continue it.
Suddenly, I found that the character "여" moves from the Blue circle into the Red circle out of blue.
Finally, as you can see at screenshot, it reads "w여ith".

This is a mess.
This was happened several times for me and I have heard this was happened a lot from others.

It should be fixed in the near future - or immediately.

regards