Reorder staff symbols when durational symbols are regrouped under new beats on symbol removal


When a durational symbol is removed from the composition data the following durational symbols may be shifted back to fill emptied space. The order of staff symbols must reflect this change, because ignorance can lead to layout failures.
Bug Reconstruction:
  • On a single staff put 8 eighth notes to the 1st voice and 4 quarter notes to the 2nd voice
  • Delete the 2nd quarter note
    => The horizontal layout is wrong. The problem is in the incorrect order of core symbols in the staff. The quarter notes that follows the previously deleted note must be shifted back to lower indices in order for the beat cluster to locate them correctly.