This problem has now seemed to resolve itself!
I never did get a chance to reboot the ASE because of my large CREATE INDEX still going. But today when I re-tested the condition, everything's back to normal. I am certain that I am testing this in the exact same way I was previously (as described in the original post).
The only change I can think of is that the CREATE INDEX just completed. It was rebuilding a clustered index on a table with 120,000,000 rows, so it ran for a couple days. It "seems like" the dbo-prefix glitch was not present before I started building that index (though without a time machine I can't be positive), and it's definitely not present now that the index is built. But it seems like DURING the time the index was being built is when the symptom was present. Is that possible?
Anyway, I am now a happy camper, though I wish I understood what this was all about.
Thanks.
- John.