I'm just using plain text converted to buttons for navigation on my menu. If I duplicate a button, then change the text on the new one, the overlay highlight text does not change - it stays the same as the duplicate.
Right. It's not the most intuitive, but what happens is that the highlights are actually separate Photoshop layers. Those aren't attached to the text in any way after they're created, so changing the text won't change the highlight.
Two ways to fix this:
1. Right-click on the button > Convert to Object. In the Layers palette, open up the button's folder, select the highlight layer, and press the Delete key. Then convert the text to a button again.
2. Wait until you have all of your text objects created, then convert them all to buttons.