I had teh smae invisible button problem using Slackware 10,
I'd compiled dvdauthor-0.6.10 from source, it all looked ok....
In the end I tracked it down, I tried dvdauthor-0.6.9 but that was the same,
but I tried dvdauthor-2773 (the latest alpha I could find) and that works,
not perfectly, there's some slightly weird buttons in the first column,
but hey, I can see the buttons now!!!!
hope this helps
gunga