On the topic of an updated R81.10 installer, I just tested something. I built a VM with the R81.20 ISO. I updated CPUSE, imported the R81.10 CPUSE package, and ran 'installer clean-install <R81.10 package>'. It left me with a working R81.10 system with the fixed R81.20 partition layout.
I accidentally installed a jumbo before running config_system, so I'll need to rebuild it before running performance tests. Still, if there's no fix for R81.10 directly, at least this should work for people who can't migrate to R81.20 yet.
Edit: Confirmed this also works for R80.40. I assume R81 as well.