In the layout editor changing the title of the "What's New" box does not change the title on the page it is on. Other box titles change just fine. It seems to be just the "What's New" box.
The "What's New" is coded in the "page content" because it is part of the newsfeed. It's not a widget. You would need to go into the code to change the wording of that.
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voteLayout Editor What's New title wont change