With input-method-unstable-v2, it's impossible to finish preedit texts
before deactivate.

    I think this is a bug in IME. Focus changes deactivates the
    input-method and I think there is no way to know it is going to be
    deactivated in advance. Which means IME does not have chance to
    commit string to old text-input. Also, by the protocol, there is no
    way to distinguish the text-input behind. With these, I think IME
    should reset their internal states (for example, to-be-committed
    string) on deactivate. This is what my wlchewing does, and so it
    does not have this bug.

    @xdavidwu

Reference:
  swaywm/sway#4932 (comment)