The Aggregator module requires that all contained modules come after it in the rendering sequence so it can properly render them inside the Aggregator instead of their current positions in the page. When the Aggregator is moved to another position, it hasn't had a chance to reset the tab order and position of the contained modules yet. Also, the DNN framework caches the tab module positions and hasn't updated itself yet. To remedy this, click on Manage Aggregator and then click Update. This should reset the tab cache and reset the positions to within the Aggregator.