hehehe, found solution:
1) only add video to dvd ONCE
2) when creating video buttons on timeline, *MUST* specify same video as self (eg PLAY ALL track), and then option for specific chapter is available
no need for all the hassle of adding video multiple times, and changing in/out points etc
nice!
downside is that the video needs to be recompressed due to the buttons, so better to bring it into DVDA as .AVI