Last several reads are not seen in the Sanger Reads Editor overview

Scenario:

1. Open "_common_data/sanger/alignment.ugenedb".
2. Collapse all rows. Make sure all rows are visible in the name list (without a vertical scrollbar), there is a vertical scrollbar in the overview.
3. Scroll the overview down.
   Expected state: reads from the first one to the last one can be seen.
   Current state: several last reads are not shown.