Heh. Heh. Heh. Let me requalify this and say that "label reads worked, but
other odd things seem to be happening"....

The latest is that some attempts to fsck a device get this failure:

sd4(ncr0:1:0): error code 0

This looks to be due to corrupted sense data getting reflected back.
I'll check into this more fully and report back a bit later today.