attempting to install alongside using canary installer; can't add partition

Ubuntu Desktop canary ISO install on
- hp dc7700 (c2d-e6320, 5gb, nvidia quadro nvs 290)

The system had a Lubuntu kinetic ISO installed; default full disk install.

Booting the Ubuntu Desktop Canary installer; the following was done

- started installer; realized it cannot shrink existing install; so exited
- opened gparted to shrink /dev/sda1 partition to create space
- restarted installer & tried to install to space beyond /dev/sda1

** Actual result

The + to add new partition is shadowed, and wouldn't do anything, I could only change the existing install

** Expected result

The + would allow me to use the created space to add a new partition for my wanted "install alongside" equivalent install.

(filed on web page as `ubuntu-bug` just gives GDK 3.0/4.0 errors then apport-collect is run)

--- Details on Window

/dev/sda 75GB disk msdos
  /dev/sda1 ext4 44GB

I was trying to use the free (~31GB) space to create partition; but I can only change existing /dev/sda1 partition, not use the + to add new partition using space.