May there be an incompatibility, if UDFIO has been initialized before, by another ELF, like (exec-)loader2 in FMCB.
I though about the optional ESR, which also implies the Fastboot.
If ESR couldn't differ between DVD-Video and ESR-Game, FMCB should do it, before ESR starts, so it may init UDFIO, if DVDV detected, to test for SYSTEM.CNF itself.
But if ESR will do it in future, that's not necessary anymore for FMCB.
PS2 V7/DMS3 V2 (FW:2.4b7); Seagate Baracuda 200GB
PS2 V7/CC1.0 (FW:34 hacked v2 BM:2.1.6); Maxtor DiamondMAX9 PLUS 160GB
PS2 SCPH-30004R; NoMod+NoLaser
3xSony MC 8MB
MAX/Datel 16MB with Boot-CD
Custom FMCB 1.8b+ Beta-Build, my AIO 0.5, Sony&xRhino-Linux