I contacted URC and sent them my misbehaving MX-890 file. Of course, I got a reply saying that they cannot offer support to an end user. So I replied that I did not expect or want personal support, but that it might be in their best interest to investigate the issue for the potential future benefit of all their clients.
I received an unexpected but welcome response three days later:
*************** Hello,
We were unable to replicate the issue here on old mx-890 files but the engineer checked out your file and it seems it was somehow corrupt and had duplicated object IDs. In an upcoming CCP update the software will perform a check of the file when opening it, just in case. If it does find errors the software will give the option of repairing the data. This is expected to be extremely rare. I have attached a repaired version of the file.