Worked on the handsontable/handsontable repository to address a critical issue in the NestedRows plugin, focusing on preventing duplication of child rows during drag-and-drop operations. Utilized JavaScript and plugin development skills to adjust dataManager.js, ensuring accurate identification of parent row indices during synchronization. Developed targeted tests for dragRow and dragRows functionalities, enhancing test coverage and reducing the risk of regressions. The work stabilized nested data manipulations and improved data integrity, minimizing edge-case failures in nested row movements. Emphasized thorough testing and precise bug fixing, resulting in more reliable user operations and a reduction in user-visible bugs within the plugin.