Just noticed a bug.
Make a vertical selection (alt+shift + down_arrow a few times). Now the first character in each row is highlighted, and the caret is blinking in front of the first character on the bottom line.
Type a character. It will insert the character in front of each line. Highlight will move to the right (so highlighting the same characters as before). Blinking caret will also move one to the right.
Undo (ctrl-z). Typed character will disappear. But highlighted column will now be 1 to the right of where it was. Caret is blinking in the right spot though.
Type a character. Now it will insert in the wrong place (where the highlight was).
