Undo option works incorrect in MSA editor

Undo button works through time(через раз)

1. Open document _common_data\scenarios\msa\ma2_gapped.aln
2. Select first symbol in first sequence
3. Click "space" 3 times
4. Click "undo" button 3 times
Expected state: Spaces are deleted
Found state: first undo deletes one space, second undo does nothing, third deletes, fourth doesn't delete etc.