Full-Width characters confuse the cursor

[hellerve]

Fullwidth characters, such as kana (e.g. なんでやねん) or even fullwidth roman characters (e.g. ｏｈ ｎｏ) confuse the cursor: it gets place at a normal halfwidth position, which is obviously wrong. Example:

This does not affect the capabilities of editing such a text, but the application still becomes more or less useless, because the cursor position is not correct.