Regression: a selected region is reset when context menu is opened

Scenario:

1. Open "_common_data/scenarios/msa/ma.aln".
2. Select any region.
3. Right-click on this selected region.
   Expected result: the context menu appears and the selected region is not changed.
   Actual result: the context menu appears, but only ONE character is selected!
4. Again select any region
5. Right-click on empty area below all sequences
   Expected result: the context menu appears and the selected region is not changed.
   Actual result: the context menu appears, but region selection has disappeared!