Two things you may not be aware of: (1) In interactive PDF, buttons are always on top of the layout (think of a separate layer) so it generally doesn't work to expect the layering you're expecting. (2) The preview you're probably talking about is how called the SWF Preview panel. It's using a totally different kind of output—SWF (Flash) to create the preview. But SWF files handle many things in a totally different way then interactive PDF.
Thanks for your reply Steve (and nice articles on InDesign secrets btw).
Unfortunately I am aware of those two 'rules' but that doesn't help in this case. The file I've supplied only has the buttons in it and the layering can be sorted if that messes up on export. It's as if the actions of the buttons are also getting switched.
I've had this type of thing working so many times in the past, I can't begin to count, and I've also got it working with 11 buttons on the same document...it seems to be when there's only three, a gremlin comes in.
Does anyone have any ideas what I'm doing wrong or what is wrong, I'm struggling...