Delete multibytes Unicode char (NOT ascii) work strange.

[doodoori2]

There are some letters are consisting of several bytes.
(Especially Korean generally using 2 bytes for 1 character)

If user press the backspace key while typing, it expected to cancel last key pressed before. (like a undo)

but If user press backspace when the input is already completed,
it expect to delete the character left of the cursor.
It seems that the character is broken by deleting one byte.