only in patch2:
unchanged:
--- a/core/misc/tabledrag.js
+++ b/core/misc/tabledrag.js
@@ -283,15 +283,13 @@
 
         // Mark the column containing this field so it can be hidden.
         if (hidden && cell[0]) {
-          // Add 1 to our indexes. The nth-child selector is 1 based, not 0
-          // based. Match immediate children of the parent element to allow
-          // nesting.
-          columnIndex = cell.parent().find('> td').index(cell.get(0)) + 1;
+          // Match immediate children of the parent element to allow nesting.
+          columnIndex = cell.parent().find('> td').index(cell.get(0));
           $table.find('> thead > tr, > tbody > tr, > tr').each(this.addColspanClass(columnIndex));
         }
       }
     }
-    this.displayColumns(showWeight);
+    this.displayColumns(showWeight, false);
   };
 
   /**
@@ -308,26 +306,16 @@
   Drupal.tableDrag.prototype.addColspanClass = function (columnIndex) {
     return function () {
       // Get the columnIndex and adjust for any colspans in this row.
-      var $row = $(this);
       var index = columnIndex;
-      var cells = $row.children();
+      var cells = $(this).children();
       var cell;
       cells.each(function (n) {
-        if (n < index && this.colSpan && this.colSpan > 1) {
+        if (n < index && this.colSpan > 1) {
           index -= this.colSpan - 1;
         }
       });
-      if (index > 0) {
-        cell = cells.filter(':nth-child(' + index + ')');
-        if (cell[0].colSpan && cell[0].colSpan > 1) {
-          // If this cell has a colspan, mark it so we can reduce the colspan.
-          cell.addClass('tabledrag-has-colspan');
-        }
-        else {
-          // Mark this cell so we can hide it.
-          cell.addClass('tabledrag-hide');
-        }
-      }
+      cell = cells.eq(index);
+      cell.addClass('tabledrag-' + (cell.attr('colSpan') > 1 ? 'has-colspan' : 'hide'));
     };
   };
 
@@ -338,14 +326,19 @@
    *
    * @param {bool} displayWeight
    *   'true' will show weight columns.
+   * @param {Boolean} updateColSpans
+   *   Whether "colspan" attributes should be recalculated.
    */
-  Drupal.tableDrag.prototype.displayColumns = function (displayWeight) {
+  Drupal.tableDrag.prototype.displayColumns = function (displayWeight, updateColSpans) {
+    // Assumed that by default the attribute should be recalculated.
+    updateColSpans = undefined === updateColSpans ? true : updateColSpans;
+
     if (displayWeight) {
-      this.showColumns();
+      this.showColumns(updateColSpans);
     }
     // Default action is to hide columns.
     else {
-      this.hideColumns();
+      this.hideColumns(updateColSpans);
     }
     // Trigger an event to allow other scripts to react to this display change.
     // Force the extra parameter as a bool.
@@ -374,16 +367,26 @@
    * Hide the columns containing weight/parent form elements.
    *
    * Undo showColumns().
+   *
+   * @param {Boolean} updateColSpanAllTables
+   *   Whether "colspan" attributes should be recalculated for all tables.
    */
-  Drupal.tableDrag.prototype.hideColumns = function () {
+  Drupal.tableDrag.prototype.hideColumns = function (updateColSpanAllTables) {
     var $tables = $('table').findOnce('tabledrag');
     // Hide weight/parent cells and headers.
     $tables.find('.tabledrag-hide').css('display', 'none');
     // Show TableDrag handles.
     $tables.find('.tabledrag-handle').css('display', '');
-    // Reduce the colspan of any effected multi-span columns.
-    $tables.find('.tabledrag-has-colspan').each(function () {
-      this.colSpan = this.colSpan - 1;
+    // Default action - is to hide the column, so the "colspan" must be
+    // subtracted by one. If we have multiple tabledrag-empowered tables
+    // on the page, then this code will be working as many times as we have
+    // tables on the page and "colspan" for last one will be calculated by
+    // formula: "(colspan - 1) * totalTablesCount". To avoid this behavior,
+    // update the "colspan" on initialization only for table that currently
+    // in processing.
+    (updateColSpanAllTables ? $tables : this.$table).find('.tabledrag-has-colspan').each(function () {
+      // Reduce the colspan of any effected multi-span columns.
+      this.colSpan -= 1;
     });
     // Change link text.
     $('.tabledrag-toggle-weight').text(Drupal.t('Show row weights'));
@@ -393,17 +396,24 @@
    * Show the columns containing weight/parent form elements.
    *
    * Undo hideColumns().
+   *
+   * @param {Boolean} updateColSpans
+   *   Whether "colspan" attributes should be recalculated.
    */
-  Drupal.tableDrag.prototype.showColumns = function () {
+  Drupal.tableDrag.prototype.showColumns = function (updateColSpans) {
     var $tables = $('table').findOnce('tabledrag');
     // Show weight/parent cells and headers.
     $tables.find('.tabledrag-hide').css('display', '');
     // Hide TableDrag handles.
     $tables.find('.tabledrag-handle').css('display', 'none');
-    // Increase the colspan for any columns where it was previously reduced.
-    $tables.find('.tabledrag-has-colspan').each(function () {
-      this.colSpan = this.colSpan + 1;
-    });
+    // On initialization we do not need to increase "colspan" since it should
+    // be correctly set on backend.
+    if (updateColSpans) {
+      // Increase the colspan for any columns where it was previously reduced.
+      $tables.find('.tabledrag-has-colspan').each(function () {
+        this.colSpan += 1;
+      });
+    }
     // Change link text.
     $('.tabledrag-toggle-weight').text(Drupal.t('Hide row weights'));
   };