Right now, buttons can only be rendered at 72dpi, but I'm working on fixing that in the next update.
If you want an immediate fix, you can put an invisible button (empty rectangle) over a text frame that is not a button and the text frame will be rendered at the higher resolution.
To get an over state, you can put the text in a Multi-State Object (MSO) and have the invisible button trigger an "over" state in the MSO on roll over.
I should have the update available in the next couple of months.