Selection group misdrawn with hidden columns

In some cases when selecting columns, the corresponding selection group has horizontal red dashed lines drawn beyond the edge of the group.

To reproduce:
- load uniref50.fa
- select second sequence and do hide insertions
- make a rectangular selection close to the left hand side of the second hidden column region and enlarge by dragging right past the hidden column marker. Red horizontal lines appear at the top and bottom stretching several columns to the right of the mouse position.