After some more thorough testing and experimentation with the new build and code, I have two observations to make:
1. Unfortunately my earlier statement about stability seems to not be correct. I also experienced quite a few lock-ups at various points, always in-mission. Only way out when this happened was to terminate FS with Task Manager. The thing is, I did not have anything like that happening the first time I tested. I guess I was lucky the first time. The command line options I use are -glow -jpgtga -fov 0.39 -ambient_factor 80 -env -alpha_env -fps. I was testing without the music vp at that time.
2. I believe I've found a pattern regarding the music vp issue, after experimenting with the source code and changing the return of the ogg_mmio_seek() callback to -1 in ogg.cpp: Lets assume that I have two missions, A and B. Mission A has a soundtrack containing oggs, while mission B has a soundtrack containing only wav files (according to mv_music.vp). When I try to load mission A immediately, it crashes. But if I load mission B first, which is using only wav, exit mission and then try to load A, everything goes well and ogg music plays perfectly. In fact, once I have loaded mission B first, I can load as many ogg soundtrack missions as I want, no problem. I am not sure why this happens, my understanding of the sound code is really very limited, but someone more acquainted with it could probably deduct something.