Preserve row order when moving rows

app/playlistmodel.py

@@ -831,12 +831,13 @@ class PlaylistModel(QAbstractTableModel):
         # endRemoveRows and the row range must be contiguous. Process
         # the highest rows first so the lower row numbers are unchanged
         row_groups = self._reversed_contiguous_row_groups(from_rows)
-        next_to_row = to_row_number
 
         # Prepare destination playlist for a reset
         self.signals.begin_reset_model_signal.emit(to_playlist_id)
 
         with db.Session() as session:
+
+            for row_group in row_groups:
                 # Make room in destination playlist
                 max_destination_row_number = PlaylistRows.get_last_used_row(
                     session, to_playlist_id
@@ -847,10 +848,10 @@ class PlaylistModel(QAbstractTableModel):
                 ):
                     # Move the destination playlist rows down to make room.
                     PlaylistRows.move_rows_down(
-                    session, to_playlist_id, to_row_number, len(from_rows)
+                        session, to_playlist_id, to_row_number, len(row_group)
                     )
+                next_to_row = to_row_number
 
-            for row_group in row_groups:
                 super().beginRemoveRows(QModelIndex(), min(row_group), max(row_group))
                 for playlist_row in PlaylistRows.plrids_to_plrs(
                     session,

tests/test_playlistmodel.py

@@ -387,9 +387,9 @@ class TestMMMiscRowMove(unittest.TestCase):
         assert [int(a) for a in row_notes] == [
             0,
             1,
+            1,
             3,
             4,
-            1,
             2,
             3,
             4,