Drag selection border to extend/shrink selection

Enable “Drag selection border to extend/shrink selection”.

Click in line number area to select a view line in a wrapped line.

** Though the caret is blinking at the right end of the view line, the right border of the selection is actually at the beginning of the next view line (invisible till you hover mouse over it and see the cursor change).
If you make the same selection by using arrow keys, then the caret is also at the beginning of the next view line. So which behavior is correct?

** The visible top/bottom borders of the selection are not draggable.
Or where are the real top/bottom borders?