Are you using the phase 5 SCSI Kit or the DCE one? I've got a DCE version 8.5, but I always had it patched down to 8.1 with SoftSCSI from Aminet. Never had any trouble with it, but then again, only my external cartridge drives are on my SCSI chain; I don't use them very often.
I remember reading a link through Amiga University about bugs with the SCSI Kit. You might want to check there. It was in the hardware/accelerator category, if I remember correctly.
