OK, that explains it.
In Encore 1.0, VTS (timelines) are written to the disc in the inverse order in which timelines were created. When you press the Next button, the disc goes to the last timeline created.
You can sort of work around this by adding a chapter in the last half second of the timeline. What will (most times) happen is pressing Next brings the viewer to this chapter, and then the timeline end action will execute.
There’s really nothing else you can do about this, except upgrade your version of Encore, in which the problem was corrected.