MAGETWO-58220: Unable to "Add Products Manually" for Configurable product

Author: VladimirZaets

app/code/Magento/Ui/view/base/web/js/dynamic-rows/dynamic-rows.js

@@ -316,9 +316,11 @@ define([
                 }, this);
             }
 
-            this.pagesChanged[this.currentPage()] =
-                !compareArrays(this.defaultPagesState[this.currentPage()], this.arrayFilter(this.getChildItems()));
-            this.changed(_.some(this.pagesChanged));
+            if (this.defaultPagesState[this.currentPage()]) {
+                this.pagesChanged[this.currentPage()] =
+                    !compareArrays(this.defaultPagesState[this.currentPage()], this.arrayFilter(this.getChildItems()));
+                this.changed(_.some(this.pagesChanged));
+            }
         },
 
         /**