Shifting of region works wrong for last columns in alignment

1. Open 'COI.aln'
2. Scroll sequence area to the last columns
3. Move to the right last column with mouse
Unexpected state: the column remains in the same place
4. Move to the right any other region, that is close to the end of alignment
Unexpected state: the region stands on the same place if mouse
goes beyond the right border of the alignment