It seems that long time ago there was a merge error in the DefaultRowSorter.java which caused a duplication of one paragraph in the specification.

 * <p>
 * If the underlying model structure changes (the
 * <code>modelStructureChanged</code> method is invoked) the following
 * are reset to their default values: <code>Comparator</code>s by
 * column, current sort order, and whether each column is sortable. To
 * find the default <code>Comparator</code>s, see the concrete
 * implementation (for example, {@link
 * javax.swing.table.TableRowSorter TableRowSorter}). The default
 * sort order is unsorted (the same as the model), and columns are
 * sortable by default.
 * <p>
 * If the underlying model structure changes (the
 * <code>modelStructureChanged</code> method is invoked) the following
 * are reset to their default values: <code>Comparator</code>s by column,
 * current sort order and whether a column is sortable.
 * <p>