The "Load more" functionality, like the "Endless scrolling", makes request (if Ajax binding is used) for the next page. The DataSource of the ListView persists only the data returned from the last request. If the "Load more" functionality is used along with grouping then the newly loaded page will be grouped separately and appended to the end of the ListView. This is the expected behavior. If you need to avoid the multple headers then you need to refresh the ListView manually. Here I prepared a simple jsBin demo for you. Note that on every click the whole ListView is re-rendered.
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