The controller and backplane set drive IDs as part of the SAS configuration. It shouldn't change, after they are set. Did you originally create the RAID without the backplanes attached?
Anyone else have an idea? The only thing I can think of would be to recreate the entire RAID from scratch, which seems a bit drastic.
Of course, two seconds after posting this, I found the answer in the software user guide
Page 50 (62 of 156)
Select View Disk Configuration to restore the configuration from the hard disk.