Fretboard diagrams: barré deleted when separate dot is added afterwards at same position

OS: Windows 10 (10.0), Arch.: x86_64, MuseScore version (64-bit): 3.0.3.5341, revision: e06ea8e

1. Create a partial barré, say, by shift + clicking on the 4th string, 3rd fret (A#6 chord):
   
2. Now click on the 6th string, 3rd fret.

Expected result: Barré remains in position:

Actual result: Barré is deleted:

See also: #283678: Fretboard diagrams: barré applied wrongly if there is another dot already at same position. Related to #283681: [EPIC] Fretboard diagram issues.