IDE Tape Trouble on 4.10: Volume Overflow

[Paul Fuqua]

     I have an IDE tape drive, a Seagate STT20000A TR-5, which I have
used for backups with FreeBSD 3.4, 4.3, and 4.7.  I have a script that
dumps all my partitions, one after the other, and depends on "dump -a"
to notice end-of-tape and prompt me to switch tapes.
     I just moved up to 4.10 -- doing a reinstall, not an update -- and
now "dump -a" isn't detecting end-of-tape.  Instead, dump reports a
write error and there is a console message:

  /kernel: ast0: WRITE - VOLUME OVERFLOW asc=0x00 ascq=0x02 error=0x02

Is this a known problem?  What can I do about it?  (Aside from hacking
my script to use "dump -B" and "mt rdhpos" to work around it, which is
mostly functional but not entirely satisfactory.)
     I have tried building a kernel with "device atapicam" and using
/dev/sa0 instead of /dev/ast0, but for some reason writing to /dev/sa0
doesn't actually write anything to the tape, even though I can probe the
tape and move it around with mt.  (But that's another problem, or
perhaps some setup is needed that I haven't figured out yet.)
     Relevant dmesg output:

ast0: TAPE <Seagate STT20000A> at ata1-slave PIO4
sa0 at ata1 bus 0 target 1 lun 0
sa0: <Seagate STT20000A 8.43> Removable Sequential Access SCSI-2 device 
sa0: 16.000MB/s transfers

     I'd appreciate any suggestions.  Thanks.

                              pf