Ephemeral error message: "cryptsetup: unknown fstype, bad password or options?"

I activated disk encryption for my Ubuntu 15.10 64bit installation and get every time after entering the (correct) password the error message:

cryptsetup: unknown fstype, bad password or options?

But after few seconds (without any further interaction) this error message is replaced by the expected message:

cryptsetup: sda5_crypt set up successfully

That's it and the system is started.

Any suggestions what could be the problem? Is it merely cosmetic or serious?

Solution 1:

This seems to be a bug caused by a race condition: https://bugs.launchpad.net/ubuntu/+source/cryptsetup/+bug/1481536

While an official patch does not seem to be released yet, several patches are discussed and uploaded to PPAs.