Been playing around with version 3 for a bit now...been trying to do that seamless intro into first play transition, can't find delayed buttons anywhere so I can do it. Did I miss something? :(
I haven't played around with it (even installed it) yet, but I imagine this is where the new entry and loop points come in. Wherever your "entry" point in the menu is, that's when your buttons appear. Anything before that is just the menu background playing; so if you've got an intro video that you want to use, just put that and the menu background all in one file and set the entry point where the buttons should become active. Then set the loop point where the menu should return on looping.
It shouldn't do that in preview - in the testing I did, preview acted just like the burnt DVD would have acted. Are you sure you set a loop point? There should be a vertical green line on the video timeline where your loop point is.