I have a TableView with nested columns.
Observed behaviour: The parent colum's right border is about half a column to the left of the right border of the final child column.
Expected behaviour: The parent column's right border is on the same pixel as the right border of the final child column.

This gets especially nasty with more than one parent column:
Observed behaviour: The final child column of the first parent and the first child column of the second parent overlap.
Expected behaviour: The final child column of the first parent and the first child column of the second parent are adjacent to each other.