Bug fixed in the method updateRecord.

static/plugin_dbui/src/appform.js

@@ -333,7 +333,9 @@ App.form.FormPanel = Ext.extend(Ext.form.FormPanel, {
                 // property format.
 
                 case 'datefield':
-                    value = value.format(field.format);
+                    if (Ext.isDate(value)) {
+                        value = value.format(field.format);
+                    }
                     break;
 
                 // For foreign key, the record contains the valueField