MSA Editor doesn't allow selection of sequences that are not visible

Scenario to reproduce:

1. Open "data/samples/CLUSTALW/ty3.aln.gz".
2. Select a sequence that is two sequences above the last visible sequence in the name list area.
3. Press and hold "shift" key.
4. Click "down" key twice.
   Expected state: three sequences are selected, the msa is not scrolled down.
5. Click "down" again.
   Expected state: four sequences are selected, the msa is scrolled down for one line.
   Current state: the state is not changed.