I can confirm this bug still exists with the most recent stretch version as well as the testing version of buster rc1.
I ran into this issue when I was provisioning a HP DL380p G8 with a HP Smart Array P420i RAID Controller. I was provisioning the machine with a live boot initrd + kernel. Both OS versions with firmware cpio.gz appended to the initramfs. The RAID controller is configured to only expose a single device (showing up as /dev/sda in the installer shell). Manually formatting the machine in the installer was not an option and the installer cannot be continue at this point unless you manually partition the drive in the shell. Provisioning Ubuntu 18.04 and 19.04 on the same machine worked just fine with the exact same method.