I've always hooked into the "demo game" routine to run my games. I'm not entirely surprised the vblank hack is causing issues.Here's iq_132's comment about the NeoSD:
Code:_vblank_callback ori #$2700, SR ; first item in vblank clr.b $300001 ; kick watchdog move.w #$7, $3c000c.l ; ack irq cmpi.b #$1, $10d2ff ; have we gone through init process? bne.s _dont_use_game_vblank ; no, jump to $122 ; do game vblank here