Pressing "Delete" button in "Search for" in the "Search in Alignment" tab

Scenario:

1. Open an alignment that contains "ACT" substrings (e.g. "COI.aln").
2. Open "Search in Alignment" tab on the options panel.
3. Enter pattern "ACT".
   Expected result: some results are found, the first result is selected in the Sequence Area.
4. Move cursor to the middle of the pattern after character "A".
5. Press Delete key on the keyboard.
       Expected result: pattern has been modified, it is now "AT".
       Actual result: the region selected in the Sequence Area is deleted.