When I type one Japanese character into Editor,
Editor seems like as follows:
-------------------------------
[JA]I
-------------------------------
    I = caret (insertion point)
 [JA] = one Japanese character.
(see attached screenshot, no1.png) 

caret is placed just next to Japanese character

Then, type three more Japanese character,
Editor seems like:
-------------------------------
[Ja][JA][JA][JA] I
-------------------------------
                 ^caret

You can see small gap between caret
and last Japanese character.
(see attached screenshot, no2.png)

Then, type 6 more Japanese character,
it seems like:
----------------------------------------------
[JA][JA][JA][JA][JA][JA][JA][JA][JA][JA]    I
----------------------------------------------
                                            ^caret


You can see more gap between careet
and last Japanese character...
(see attached screenshot, no3.png)



It happned only Mac OS-X and default setting.

Default font setting for editor is
"Monospace / Standard / 13".
If I changed font setting from this
to Japanese font such as
"Osaka / Standard / 13",
I cannot reproduce this problem.

So, It seems workaround of this problem, I think.