Doing a test install, this time I actually read the "Review options before installation" page. I decided to use existing partitions (but re-format them): sda1 as swap and sda2 as ext4 root. Now the "Review options before installation" page under "Installation" shows "Use sda1 as swap" twice:

Format /dev/sda2 as ext4 root partition
Use /dev/sda1 as swap swap partition
Use /dev/sda1 as swap partition

I guess the line in the middle should read "Format /dev/sda1 as swap partition" instead.