To reproduce, use an arbitrary tableView with enough columns such that some are off the viewport (f.i. the example provided for JDK-8213540),

- adjust such that hbar.value == 0
- drag first column to the right until it's off the viewport

Now note two issues:

A:
- expected: viewport scrolled such that the target column is visible
- actual: no scroll, dropping happens "blind"

B:
- expected: reorderingLine moved off the viewport
- actual: reorderingLine sticks to last target column that's visible, thus being useless as visual hint to the target