David, excellent questions.
I am exporting to Acrobat with interactive settings (bookmarks, etc.) checked, highest quality, etc. and viewing in Acrobat Pro X on my PC. As for other things sitting on top of the hidden buttons, I thought of that, too, and placed all buttons in their own, top layer; and I am certain there are no other objects on top of them.
Another weird thing: For diagnostics, I tried a couple tests. First, I tried to repurpose one of my working buttons from Go To Destination to Next Page. The button will not convert to any other action. After exporting, it reverts to its original, working, Go To Destination. Next, I tried just copying that working button and placing the extra copy over my Next triangle shape. It doesn’t work (BTW, the mouse cursor remains an arrow over the new object. It doesn’t morph to the pointy finger as it does over the working buttons). I then tried taking that copied button off of the master page and pasting directly on the first page of my document. Still nothing.
It seems as if I have hit the top end limit of the number of interactive objects allowed in a document. Is this possible? But then, I also tested by creating a new, fresh document of 5 blank pages, with nothing on them but page numbers and Prev Next buttons. I cannot get those buttons to work, either. So, it does seem like operator error here. I stumbled into doing something right with my menu and now I’m missing a step(s) with the Prev Next buttons!