Comment 11 for bug 1205397

(No idea if posting to the right place, hopefully someone, somewhere out there gets some use out of this. It's far too rare for me to go back and actually post solutions to problems I had and fixed..)

I had the same problem, there's definitely something wrong with the installer (I was trying to set up 14.04 with encrypted partitions on different drives, with / on my small SSD and /home /usr /tmp /var and swap on my HDD). But I played around with it, restarted the installer/rebooted a number of times, and here's how you work around it:

It's the ordering. It can't cope with setting swap as an encrypted partition and then creating another partition after that. So, set up all your actual partitions, including your encrypted containers first. I believe it necessary to include an encrypted partition for swap, so make sure to make one of suitable size for it. Don't know if relevant, but I happened to pick all logical partitions and that worked.

Once you have them all set up, THEN, and only then pin them to actual mount points (setting this straight away will result in a crash). I started with swap and then moved on to /home and so on.

Now you have your encrypted partitions, and you don't have to forgo swap with swapoff!