Look at the attached movie.

When I try to resize the most right column, some jump happens, and the border (which must be under the cusror) is shifted right on approximately 20 pixels, and there a distance, between cursor and a border.

After that, I scroll to the end, and you can see a graphical artefact upper the vertical scroll bar. (wrongly evaluated position of the border of columns' headers).

This is actual, as I saw, for simple column, not only for nested.