All right, I finally got around to looking at this again, and, as expected (by me, even) there was a stray pixel or something in the highlight layer. I did a ⌘-T to get a transform bounding box in PS, and saw that for the highlight layer, it went way off to the left. Weird. So I then highlighted the area where I thought it might be and applied a Hue/Saturation to see if I could bring it out a little, since I couldn't see it. I tried raising and lower the brightness with a transparent background, a white background, and a black background. I couldn't see it on any background, even zoomed in to 800%. I still don't know what it was, but I just drew a marquee around the highlight that I wanted, inverted the selection and deleted, and now the bounding box for the button is as it should be in Encore.
The extra weird thing is that this seemed to happen on random buttons in my design. In PS, I would create a new button group by duplicating the one above it, then move it straight down below the previous button. I replaced the text and then moved the highlight a bit to the left or the right to be in the correct spot in relation to the new bit of text. And that duplicted layer group which had the correct bounding box with no extraneous bits in the highlight layer would then all of a sudden have the incorrect bounding box and apparently some little bit that PS could see, though I couldn't. Strange.
So, still a bit mysterious, but thanks for your help and ideas.
