Mmmmm…not sure why it’s going to the root menu of VTS 1. Pretty simple fix here. Instead of going to a menu in the VGM, go to a Title first (TT which is good practice anyway to prime your player buffer).
In the track editor put a chapter (PG) 1 sec before the end of the track. Then disable your UOPS for “Next” & “Previous” for that final PG (chapter). Here’s how it will work:
First Play – VTS 1(TT1) – post command main menu. When your client hits next during the “Open” they will skip to that chapter you put in there, then immediately (1 sec) post command up to the VGM where your Main Menu sits.