Can not add partitions to existing 3ware RAID?

[Michael R. Wayne]

Tonite I was going to allocate some more disk space to a 6.1 RELEASE
system.  I did it the same way I've done it for years:  I went into
sysinstall, selected
   Custom->Partition
and added a new partition (twed0s3) using some of the remaining
space.  I then moved up to twed0s1 and did an "S" because
sysinstall never remembers that the first slice was bootable and
not doing this leaves one with an unbootable system.

I then do a "W" to write out this information, say "Yes" to the
warning since I am modifying an existing system and select the
Standard Boot Manager.  Instead of the normal response, I get
   ERROR: Unable to write data to disk twed0!
and
   Disk partition write returned an error status!
which is most disconcerting.

No messages in the logs or on the (serial) console.  Checking
sysinstall again, the disk remains unchanged.

Has something recently changed in this process?

/\/\ \/\/