Hi Yutaka,
I see. When lines wrap by window, things get complicated.
How about disable this automated feature when wrapping is on? because normally when a user makes a vertical selection when wrapping is on, he is not trying to append each line, since visually his cursor is not all at the end of each line but partly in the middle of some lines.
So, this automated feature will only be enabled when:
1. line wrap is off.
2. vertical selection of zero width at the right of the end of all lines.
what do you think? :-)