Sorry for not following up on my post earlier. I don't have much of a clue about DVD Lab, so I'll let ReverendBeastly advise you on that front. I'm sure you're not doing anything wrong, and every disc seems to have some compatibility issues (even the Matrix!).
Coming from a different direction with regards to the authoring, there is nothing in the DVD Spec for a 'Still Track'. Spruce Maestro offers you menus that are stills, loops or play onces and divides your assets into either menus or movies, and even this is quite an abstraction layer. Scenarist just gives you the option of PGCs which you build up as either tracks with navigation and highlights (menus) or not (movies). I'm a bit rusty on Scenarist, so someone may correct me there.
As far as I'm aware, you can make a still have a duration up to 254 seconds. At 255 seconds the DVD Player will hold the image infinitely. With regards to audio, I believe you must always have some sort of video in a track (I know Spruce throws up an error if you don't).
What I'm trying to say in a roundabout way is that perhaps DVD-Lab is doing things behind the scenes which are causing these issues people are experiencing. As I said, it sounds like Reverend Beastly will be able to help you with more specifics, but I thought knowing the in's and out's and behind the scenes might also be of help.