Incorrect behavior of MSA Editor with one-lined alignment

1. Open {_common_data/scenarios/msa/ma_one_line.aln}
2. Set the cursor to the end of line.
3. Insert four gaps with SPACE.
4. Set the cursor to the beginning of line.
5. Delete one symbol with DELETE.
   Expected state: line length is 15.
   Current state: line length is 11, the end of line is not visible.

Note, if you add some new gaps, UGENE will show all hidden symbols. Also, you can use undo/redo buttons to see hidden symbols.