Welcome to the forum. You sound like an experienced and thoughtful user. There is one case that surprised me the first times it happened that is a bit different from other programs: BIAB treats songs without melody .SGU and songs with melody .MGU differently. When you have been working without a melody and then add one, it becomes a new file. Could this be what you are experiencing?


BIAB 2026 Win Audiophile. Software: Fender Studio One 8, Swam horns, Acoustica-7, Notion 6, Song Master Pro, Win 11 Home. Hardware: Intel i9, 32 Gb; Presonus Quantom HD8 & Faderport 8, Royer 121, Adam Sub8 & Neumann 120 monitors.