Alignment length is reduced on gap removing with Backspace, but the reference length is not reduced

Scenario:

1. Open an alignment of Sanger reads, where position of the last character in a read is equal to the reference length.
2. Select this character.
3. Press the Space key.
   Expected state: a gap is inserted to the read before the last character, the alignment length is increased, a trailing gap is added to the reference.
4. Press the Backspace key.
   Current state: the gap is removed, the alignment length is reduced, but the reference length is not reduced. You can select the trailing gap in the reference with the keyboard.
   Expected state: the alignment length shouldn't be reduced. Or the trailing gap should be removed, if UGENE-5740 is done.